What Is The Most Convenient Location To Tap Into The Speed Sensor Wire

[silvercorvette]

I am not happy with the Lexus NAV and decided to buy and aftermarket dash unit. It is a Garmin SP 7500 with dead reckoning. I don't think there will be many situations where I will need the dead reckoning but I would like to install it because it was included with the Garmin. I assume that since I am not trying to disconnect the speed sensor it will be easier because I should be able to tap into the wire at any convenient point. Is there someplace under the hood or maybe under the dash by a fuse panel where I can use a wire tap? A tap and squeeze connector like this

http://www.radioshack.com/product/index.js...rentPage=family

should make it easy to install I just need to know what the easiest place is to tap into the wire.

[dcfish]

I am not happy with the Lexus NAV and decided to buy and aftermarket dash unit. It is a Garmin SP 7500 with dead reckoning. I don't think there will be many situations where I will need the dead reckoning but I would like to install it because it was included with the Garmin. I assume that since I am not trying to disconnect the speed sensor it will be easier because I should be able to tap into the wire at any convenient point. Is there someplace under the hood or maybe under the dash by a fuse panel where I can use a wire tap? A tap and squeeze connector like this

http://www.radioshack.com/product/index.js...rentPage=family

should make it easy to install I just need to know what the easiest place is to tap into the wire.

The speed sensor wire is violet/white pin 10 on the lL3 connector, I beleive you will find it behind the glove box. Behind the right kick panel.

You really owe me a beer I usually never help with aftermarket.

SPEED_SENSOR_DASH_WIRING.pdf

[silvercorvette]

Thank you very much, I don't mean to put down the Lexus, as a matter of fact I have owned more cars than I can count and the RX400H is one of my top five. I don't regret getting the Lexus NAV because it part of a multi feature (Camera, calender, etc) package. But I have made a few trips including one from TX to NY with a Garmin 2610 on the dash board and the Lexus NAV turned on and the Garmin preformed better. But the maps on the Garmin were outdated so instead of upgrading the maps I bought a new GPS system. Now that I have the DRL turned off and I will soon have my new NAV in it I feel the the RX400H is as close to perfect as you can get.

[dcfish]

Thank you very much, I don't mean to put down the Lexus, as a matter of fact I have owned more cars than I can count and the RX400H is one of my top five. I don't regret getting the Lexus NAV because it part of a multi feature (Camera, calender, etc) package. But I have made a few trips including one from TX to NY with a Garmin 2610 on the dash board and the Lexus NAV turned on and the Garmin preformed better. But the maps on the Garmin were outdated so instead of upgrading the maps I bought a new GPS system. Now that I have the DRL turned off and I will soon have my new NAV in it I feel the the RX400H is as close to perfect as you can get.

Always willing to help a fellow lexus owner Are you going to remove the factory nav ? Do you want the factory headunit with cd controls ?

[silvercorvette]

It is a lease so I have to return it with everything that it came with. But Even if I didn't have to, I still like the other features that you need the NAV screen to access. I guess simple things amuse me because I enjoy looking at the car display that has the power consumption record for the past 30 minutes, and the hybrid battery charge display that changes colors. So even though I had to buy and after market GPS I am still happy with the NAV option, By the way the rear view camera can be hooked up to the Garmin but I like having in the NAV display the3 rear view. The Garmin also has a feature that I like, it displays traffic tie-ups. You can do it if you install the XM radio in the Lexus but I tried SAT radio and didn't like it and the XM set is a lot more expensive. The Garmin has a XM radio built in so you can get traffic reports but you must pay for the XM and add on the traffic report for an extra fee. But with the Garmin you can buy an antenna that will change the colors of the roads to represent the traffic flow. You get 15 months free when you buy the antenna for the Garmin and after that it is $60 a year (a lot less than the XM radio traffic fee)

[wwest]

It is a lease so I have to return it with everything that it came with. But Even if I didn't have to, I still like the other features that you need the NAV screen to access. I guess simple things amuse me because I enjoy looking at the car display that has the power consumption record for the past 30 minutes, and the hybrid battery charge display that changes colors. So even though I had to buy and after market GPS I am still happy with the NAV option, By the way the rear view camera can be hooked up to the Garmin but I like having in the NAV display the3 rear view. The Garmin also has a feature that I like, it displays traffic tie-ups. You can do it if you install the XM radio in the Lexus but I tried SAT radio and didn't like it and the XM set is a lot more expensive. The Garmin has a XM radio built in so you can get traffic reports but you must pay for the XM and add on the traffic report for an extra fee. But with the Garmin you can buy an antenna that will change the colors of the roads to represent the traffic flow. You get 15 months free when you buy the antenna for the Garmin and after that it is $60 a year (a lot less than the XM radio traffic fee)

Why would ANY GPS system need a speed input from the "carrying" vehicle? If the GPS cannot compute the vehicle speed in REAL TIME without such a connection then something is VERY wrong. I have a 2001 AWD RX300 with Nav but always rely on my portable Garmin as it is far more reliable in finding the most direct route whereas the RX's nav system only "finds" the new, correct, (shortest distance, etc.) route as I follow the garmin directions.

[silvercorvette]

Apparently you don't know what dead reckoning is. You need to be connected to the speed sensor to have D/R work. I type very slowly so rather than explain dead reckoning I'll see if I can copy and paste instead of typing an explanation

[silvercorvette]

OK I found a few sites that explain what D/R = Dead reckoning is and why it is good to have a GPS with D/R (By the way the Lexus Nav has D/R built into it). Here is a short explanation of what D/D is

dead-reckoning capabilities, so you'll continue to get navigation guidance even when GPS signals are obscured. To use this feature, a special dead-reckoning cable must be connected to your vehicle's speedometer and backup lights by an authorized Garmin installer. Once installed, your StreetPilot will acknowledge your turns as well as your distance traveled when GPS reception is unavailable. Driving with dead reckoning is so seamless you won't even know if you happen to have lost GPS reception.

*************************************************************************************

The D/R not only utilizes a speed sensor it also has a solid state gyro built in to it so it knows when you make a turn when your satellite signal is blocked.

This site gives a very detailed explanation of what D/R is and how it works. I has more info than you would ever want to know but it is very interesting if you are kind of geeky like I am

http://www.gpsworld.com/gpsworld/article/a...70&pageID=1

[silvercorvette]

One other thing, you are confused about what a GPS does. The SAT receiver locates your position and uses the SAT signals to get a fix on where you are. But as far as finding a route, that is dependent on the software algorithms. The software finds you at point "A" and then locates point "B" and then figures out the best way to get there. Some programs work better than others. On my last trip from TX to NY I had my old Garmin on the dash while I turned on the Lexus NAV. The Garmin was able to figure out a shorter route.

Getting back to D/R, once the GPS figures out where you are it will keep you on track as long as it continues to recieve a SAT signal, but what happens if you lose the signal for a long period of time? I have gotten into situations where the SAT signal was lost due to a lot of trees but hat normally isn't a big problem. When you lose the SAT signal in a city with tall building it can be a big problem That is why it is good to have the D/R because it will keep fixed on your position even if it has no signal. In my opinion the most important place to have D/R is if you are in a city with tall buildings and are likely to lose the signal. There is a good chance you can miss and important turn if you lose the signal and don't have D/R. I have been in situations where vandals tore the street sign down and I came to an intersection with no indication of what the cross street was. With D/R it will identify the name of the street even if you ave lost the Sat signal. I hope that explains why you need D/R and why it needs to be hooked up to a speed sensor.

EDIT

This isn't a good example of the benefits of D/R but Here is something I noticed going through the Holland tunnel in Manhattan. When I entered the tunnel the old Garmin I had without D/R lost my position while I was in the tunnel and when I got out of the tunnel it took a few seconds to find itself after it locked into the SATs. But The Lexus with D/R knew exactly where I was in the tunnel at all times using the D/R. I course this is a poor example because you don't make any turns in a tunnel and there is only one place where you will exit. But as I said before what happens if you loose your SAT reception and you are coming to a turn. If you don't have D/R the odds are you will miss the turn, and things are even worst if you are in NY city where most of the street signs are missing.

[wwest]

One other thing, you are confused about what a GPS does. The SAT receiver locates your position and uses the SAT signals to get a fix on where you are. But as far as finding a route, that is dependent on the software algorithms. The software finds you at point "A" and then locates point "B" and then figures out the best way to get there. Some programs work better than others. On my last trip from TX to NY I had my old Garmin on the dash while I turned on the Lexus NAV. The Garmin was able to figure out a shorter route.

Getting back to D/R, once the GPS figures out where you are it will keep you on track as long as it continues to recieve a SAT signal, but what happens if you lose the signal for a long period of time? I have gotten into situations where the SAT signal was lost due to a lot of trees but hat normally isn't a big problem. When you lose the SAT signal in a city with tall building it can be a big problem That is why it is good to have the D/R because it will keep fixed on your position even if it has no signal. In my opinion the most important place to have D/R is if you are in a city with tall buildings and are likely to lose the signal. There is a good chance you can miss and important turn if you lose the signal and don't have D/R. I have been in situations where vandals tore the street sign down and I came to an intersection with no indication of what the cross street was. With D/R it will identify the name of the street even if you ave lost the Sat signal. I hope that explains why you need D/R and why it needs to be hooked up to a speed sensor.

EDIT

This isn't a good example of the benefits of D/R but Here is something I noticed going through the Holland tunnel in Manhattan. When I entered the tunnel the old Garmin I had without D/R lost my position while I was in the tunnel and when I got out of the tunnel it took a few seconds to find itself after it locked into the SATs. But The Lexus with D/R knew exactly where I was in the tunnel at all times using the D/R. I course this is a poor example because you don't make any turns in a tunnel and there is only one place where you will exit. But as I said before what happens if you loose your SAT reception and you are coming to a turn. If you don't have D/R the odds are you will miss the turn, and things are even worst if you are in NY city where most of the street signs are missing.

If you need to use the vehicle speed sensor for D/R during the short periods of loss of GPS signals then you may be in a LOT more trouble than you think. First of all, GPS will continue to display the computed speed, a computed speed which in all likelihood will be more accurate (not suject to tire inflation level, etc, etc.) than any vehicle speed sensor readout.

Makes me begin to wonder how I survived my early days of flying mostly D/R cross-country relying on a compass and an airspeed indicator, and airspeed indicator mostly based on "guesstimated" atmospheric pressure.

And if you need D/R while driving through the Holland tunnel then you really are in TROUBLE.

The most I have ever encountered as to loss of signal was for a few miles in the mountains here and there in the quite beautiful Pacific NW. But even then unlike flying I had the roadbed to rely on for those few miles instead of having to begin a D/R computation sequence.

And by-the-by I specifically said "the Rx's nav system" with regard to routing, not GPS.

[skyfish400h]

I course this is a poor example because you don't make any turns in a tunnel ...

Thanks for the primer on Dead Reckoning with a GPS system. This feature is quite valuable and contributes greatly to Information Assurance coming from the NAV screen. It gives the driver the best possible information on position above and beyond the GPS alone.

Comparing the Garmin and the Lexus however is not apples and apples since the Lexus D/R system uses more than just speed to calculate position. It also used steering input. This helps in the case where you are driving in downtown among tall buildings and making turns. The Garmin would have you going in a strait line from your last known position and the distance would be a function of your speed and time elapsed.

That said, I've experienced D/R with the Lexus and its steering input and at least for freeway exits it does not work very well. That is probably because the steering inputs are small but can result in large changes in heading. I basically got the Garmin equivalent D/R which had me continuing along the freeway even tho I had made a 45 deg change in heading. It probably works better in downtown city streets where turns are more obvious and speed change can be better correlated with turning inputs to figure out where the car is going. My few times in that situation have never left me unsure of my position and there is a great possibility that I was out of contact with the SAT GPS signal.

[RX400h]

I used my father's Garmin NUVI 660, about a month ago and I prefer the Lexus Nav system, primarily because it provides more verbal info and thus, allows more time to change lanes, make corrections, etc. The Garmin has some good features as well, but as far as the info coming from the woman's voice guidance, the Lexus wins by a good margin, IMO.

[silvercorvette]

One other thing, you are confused about what a GPS does. The SAT receiver locates your position and uses the SAT signals to get a fix on where you are. But as far as finding a route, that is dependent on the software algorithms. The software finds you at point "A" and then locates point "B" and then figures out the best way to get there. Some programs work better than others. On my last trip from TX to NY I had my old Garmin on the dash while I turned on the Lexus NAV. The Garmin was able to figure out a shorter route.

Getting back to D/R, once the GPS figures out where you are it will keep you on track as long as it continues to recieve a SAT signal, but what happens if you lose the signal for a long period of time? I have gotten into situations where the SAT signal was lost due to a lot of trees but hat normally isn't a big problem. When you lose the SAT signal in a city with tall building it can be a big problem That is why it is good to have the D/R because it will keep fixed on your position even if it has no signal. In my opinion the most important place to have D/R is if you are in a city with tall buildings and are likely to lose the signal. There is a good chance you can miss and important turn if you lose the signal and don't have D/R. I have been in situations where vandals tore the street sign down and I came to an intersection with no indication of what the cross street was. With D/R it will identify the name of the street even if you ave lost the Sat signal. I hope that explains why you need D/R and why it needs to be hooked up to a speed sensor.

EDIT

This isn't a good example of the benefits of D/R but Here is something I noticed going through the Holland tunnel in Manhattan. When I entered the tunnel the old Garmin I had without D/R lost my position while I was in the tunnel and when I got out of the tunnel it took a few seconds to find itself after it locked into the SATs. But The Lexus with D/R knew exactly where I was in the tunnel at all times using the D/R. I course this is a poor example because you don't make any turns in a tunnel and there is only one place where you will exit. But as I said before what happens if you loose your SAT reception and you are coming to a turn. If you don't have D/R the odds are you will miss the turn, and things are even worst if you are in NY city where most of the street signs are missing.

And if you need D/R while driving through the Holland tunnel then you really are in TROUBLE.

I assumed that went you made your statement you didn't know what dead reckoning was and I did my best to explain it but now I realize you do know what D/R is but you still continue to pick apart my posts. I don't know if you are being purposely being argumentative or if for some reason I am not getting through to you. You made a statement about being in trouble if I need D/R in the Holland tunnel when I clearly stated that I was using the Holland tunnel to illustrate a point and I will quote myself on this "This isn't a good example of the benefits of D/R but Here is something I noticed going through the Holland tunnel in Manhattan.........this is a poor example because you don't make any turns in a tunnel and there is only one place where you will exit " . So if f I clearly stated the I was using the Holland tunnel as a poor example why are you making a big deal of the fact you don't need it in the tunnel? The Holland Tunnel wasn't a good example but I was using it to illustrate how D/R is able to keep track of where you are even though you have no signal, it was the best I could think of at the time. It was a bad example because as I stated before you can't make any turns in a tunnel, but it was also a good example because it illustrated that even in extreme conditions it can keep track of your location. After I made the post I thought of a better example, I live on Long Island 40 miles east of Brooklyn but there I times when it is necessary to drive through Brooklyn

I never stated that D/R is essential to have with your GPS system. Obviously if you live "in the quite beautiful Pacific NW" you won't be subject to the same satellite reception conditions that I do living in Long Island. There are areas in Brooklyn (Long Island) where you can drive for long distances under an elevated subway (oxymoron) and not receive a GPS signal for miles. And if you happen to be in an area where most of the streets signs are missing having D/R can greatly enhance the functionality of your GPS system. You brought flying into the discussion of driving with GPS. In many cases knowing your position while driving is more important. If I miss a street by a few feet while driving in Brooklyn because my signal is blocked by an elevated subway it may be quite difficult to get back on track because I may encounter some one way streets, streets blocked by construction, and trucks making deliveries that are blocking the road. If I I am off by a few feet while driving in Brooklyn it is a big deal missing a turn and trying to get back on track. But if you miss a turn by a few hundred feet in the air all you need to do is adjust your heading by a few degrees.. So although D/R may not be useful to a person living the quite beautiful Pacific NW this country extends far beyond the quite beautiful Pacific NW and people that drive in areas with tall buildings welcome the additional tool that D/R adds to our GPS systems to functionality

[silvercorvette]

I course this is a poor example because you don't make any turns in a tunnel ...

Thanks for the primer on Dead Reckoning with a GPS system. This feature is quite valuable and contributes greatly to Information Assurance coming from the NAV screen. It gives the driver the best possible information on position above and beyond the GPS alone.

Comparing the Garmin and the Lexus however is not apples and apples since the Lexus D/R system uses more than just speed to calculate position. It also used steering input. This helps in the case where you are driving in downtown among tall buildings and making turns. The Garmin would have you going in a strait line from your last known position and the distance would be a function of your speed and time elapsed.

That said, I've experienced D/R with the Lexus and its steering input and at least for freeway exits it does not work very well. That is probably because the steering inputs are small but can result in large changes in heading. I basically got the Garmin equivalent D/R which had me continuing along the freeway even tho I had made a 45 deg change in heading. It probably works better in downtown city streets where turns are more obvious and speed change can be better correlated with turning inputs to figure out where the car is going. My few times in that situation have never left me unsure of my position and there is a great possibility that I was out of contact with the SAT GPS signal.

The Garmin does not rely solely on the speed sensor alone to calculate position. The Garmin also has a internal electronic gyroscope to calculate turn angles

I have to confess that I am not entirely sure how the Lexus NAV system works but I suspect that it may also adjust it's directional settings from a gyroscope using the same method as Garmin. From what I know of the Garmin system it gets its (when using D/R) information using a combination of Speed input from the speed sensor and turn information from the electronic gyroscope. So when you are using D/R the GPS system is using a combination of speed input from the speed sensor and changes in direction from the gyroscope.

I have been using my Garmin 2610 for a few years and have driven with it from Key West to Springfield Massachusetts, and from LI NY to Dallas and Houston Texas and have never had it not respond to a turn (when it was receiving a signal, the 2610 does not have D/R). It has positioned me off the road but that was because the map was out dated and there was new road construction. I have driven from LI to TX a few times and have never had the problem you described with being plotted off the road. Could it be possible that the GPS was correct and there was new road construction and the new road or exit is now in a slightly different location than the old road?

[silvercorvette]

I used my father's Garmin NUVI 660, about a month ago and I prefer the Lexus Nav system, primarily because it provides more verbal info and thus, allows more time to change lanes, make corrections, etc. The Garmin has some good features as well, but as far as the info coming from the woman's voice guidance, the Lexus wins by a good margin, IMO.

I am basing my opinion on over 3,000 miles of driving with both my old obsolete Garmin 2610 and the Lexus NAV ver 6.1 in my 2007 RX400H. I drove with both turned on in trips from NY to TX. I had the Garmin sitting on the dash while I had the Lexus NAV turned on. The Garnim plotted better / shorted routes, and the Garmin found a detour route a few times when I was stuck in traffic due to construction but the Lexus NAV couldn't calculate a alternate route. I will be getting a new Garmin SP 7500 in a few days and if it works as well as my old obsolete Garmin 2610 I will be very happy

[wwest]

I course this is a poor example because you don't make any turns in a tunnel ...

Thanks for the primer on Dead Reckoning with a GPS system. This feature is quite valuable and contributes greatly to Information Assurance coming from the NAV screen. It gives the driver the best possible information on position above and beyond the GPS alone.

Comparing the Garmin and the Lexus however is not apples and apples since the Lexus D/R system uses more than just speed to calculate position. It also used steering input. This helps in the case where you are driving in downtown among tall buildings and making turns. The Garmin would have you going in a strait line from your last known position and the distance would be a function of your speed and time elapsed.

That said, I've experienced D/R with the Lexus and its steering input and at least for freeway exits it does not work very well. That is probably because the steering inputs are small but can result in large changes in heading. I basically got the Garmin equivalent D/R which had me continuing along the freeway even tho I had made a 45 deg change in heading. It probably works better in downtown city streets where turns are more obvious and speed change can be better correlated with turning inputs to figure out where the car is going. My few times in that situation have never left me unsure of my position and there is a great possibility that I was out of contact with the SAT GPS signal.

The Garmin does not rely solely on the speed sensor alone to calculate position. The Garmin also has a internal electronic gyroscope to calculate turn angles

I have to confess that I am not entirely sure how the Lexus NAV system works but I suspect that it may also adjust it's directional settings from a gyroscope using the same method as Garmin. From what I know of the Garmin system it gets its (when using D/R) information using a combination of Speed input from the speed sensor and turn information from the electronic gyroscope. So when you are using D/R the GPS system is using a combination of speed input from the speed sensor and changes in direction from the gyroscope.

I have been using my Garmin 2610 for a few years and have driven with it from Key West to Springfield Massachusetts, and from LI NY to Dallas and Houston Texas and have never had it not respond to a turn (when it was receiving a signal, the 2610 does not have D/R). It has positioned me off the road but that was because the map was out dated and there was new road construction. I have driven from LI to TX a few times and have never had the problem you described with being plotted off the road. Could it be possible that the GPS was correct and there was new road construction and the new road or exit is now in a slightly different location than the old road?

Sorry, an electronic gyroscope would undoubtedly require some sort of a SOLID/RIDID mount and a calibration procedure, something along the lines of driving in a full circle all the while the GPS signal from all three (??) satelites remains continously available. I suspect that what is happening that is misleading you into thinking you have an embedded electronic "gyroscope" (or magnetic/electronic compass, maybe) is that even with brief loss of the positioning signal your Garmin will continue to compute and update your position, map display route, based on previous speed, for at least a few hundred(??) milliseconds.

And what is it that makes you think you're loosing all three GPS satelite signals simultaneously?

I have traveled the county with a Garmin in our MH and once the signal is, signals are, initially acquired, not an always easy task in the cab of a class "C" MH, I simply don't see any tracking dropouts, certainly never to the level of the mountainous regions here in the NW.

Not really trying to argue, but to more fully understand.

So, off to the Garmin site for a morning of reading, education.

Oh, the Lexus system most definitely has an electronic "gyroscope", but they call it an electronic magnetic compass. That's wherein I derived the information that it must be ridgidly mounted and cablibrated via the method I described.

Oh, and "thirdly"....

When the Lexus system is in use I almost always have the display turned off. IMMHO the last thing I need in those instances is to be indesisive when coming right up on an intersection and be temped to devert my eyes from the roadbed, driving task, to the display at the last minute to gain additional insight. I feel it is much better, safer, to either miss my turn or simply commit to one even not being sure its correct.

In flying that's called having your mind out there about 50 yards ahead of the prop.

[wwest]

Wow....

Back from the Garmin site, multiple ones actually, and some serious research across the internet.

Two points.

1. While giving fairly reasonable explanations/procedures for correctly estabishing the proper electric connections to the vehicle, The SP-7500 owners manual quite clearly states that the D/R capability must be professionally installed.

I take that to mean, just as I would logically expect, that beyond actually making the electrical connections some sort of cabibration procedure is required. I had absolutely no luck in finding any publication or document on the internet related to the "professional" installation procedures. The only explanation I can think of for that is that Garmin does not want an end user making an installation attempt so the documentation, procedure, is being with-held from the public somehow.

2. The owners manual does not make it very clear just how and when D/R is to be used.

I did find information elsewhere that implies that it doesn't automatically switch to D/R when the GPS signals are lost, but must be manually switched into one mode or the other. Apparently, seemingly, the target market is delivery vans operating in highly congested areas. Areas wherein the vehicle speed sensor, once carefully and correctly calibrated, can be used along with a "compass", by the nav mapping database and software to track and direct vehicle position.

I think I'd try an external antenna to increase the probability of attaining a strong and relaible GPS signal long before attempting to use this device's D/R capability. Or even one of the otehr Garmin GPS/Nav devices that seeming have the higher sensitivity GPS reciever capability. $1000.00+...?? Low reciever sensitivity....?

[silvercorvette]

WWEST I apologize for any misunderstanding, but sometimes it is harder to interpret the written word than it is to interpret the spoken word because you don't get voice ques such as voice inflections and tones. .When I am wrong I don't hesitate to admit it, and I readily admit I was wrong when I felt you were purposely being a PITA. However in my mind the issue of how the D/R works still hasn't been resolved to my satisfaction and it won't be until I call Garmin and get a definitive answer. I believe an answer to the question will be helpful to people that live in cities with tall buildings. I live in the western third of Long Island and never encounter tall buildings in my area but on the rare occasions when I go into the far western end of LI and end up driving under subway tracks I can wind up driving for a few miles without a signal. If you combine the loss of signal with missing street signs and being in an unfamiliar area it could spell trouble. Last Jan when I spent time in my TX house I drove out to Dallas to see the museum where Kennedy was shot and I did wind up driving in areas where there wasn't any signal but luckily the Lexus D/R took over. Some drivers may drive in areas where they need D/R on a regular basis. In the areas I drive D/R may come into play once or twice a year or maybe one every two or three years, but if or when you need it, it could be a life saver

[wwest]

WWEST I apologize for any misunderstanding, but sometimes it is harder to interpret the written word than it is to interpret the spoken word because you don't get voice ques such as voice inflections and tones. .When I am wrong I don't hesitate to admit it, and I readily admit I was wrong when I felt you were purposely being a PITA. However in my mind the issue of how the D/R works still hasn't been resolved to my satisfaction and it won't be until I call Garmin and get a definitive answer. I believe an answer to the question will be helpful to people that live in cities with tall buildings. I live in the western third of Long Island and never encounter tall buildings in my area but on the rare occasions when I go into the far western end of LI and end up driving under subway tracks I can wind up driving for a few miles without a signal. If you combine the loss of signal with missing street signs and being in an unfamiliar area it could spell trouble. Last Jan when I spent time in my TX house I drove out to Dallas to see the museum where Kennedy was shot and I did wind up driving in areas where there wasn't any signal but luckily the Lexus D/R took over. Some drivers may drive in areas where they need D/R on a regular basis. In the areas I drive D/R may come into play once or twice a year or maybe one every two or three years, but if or when you need it, it could be a life saver

I agree, it is difficult to understand why Garmin would include such a seemingly market viable option but not provide adequate useage documentation for same. I guess I can sort of understand withholding the details of the D/R installation procedure, legal liability issues and all, but given today's level of backchannel information flow it will probably be only a matter of time before it becomes publically available."

For instance I don't think I could become very trusting of the D/R capability absent knowing how, if, the system has been calibrated or somehow automatically "learned" to correctly correlate the number of PPS from the speed sensor vs the actual distance travelled.

And were the system not automatically switching back and forth (asumption) between GPS and D/R the embedded (assumption, again) magnetic compass would need not be calibrated. But back and forth switching would undoubtedly require the compass to be calibrated, not only to magnetic north, but "around", for the full circle, of the compass "readings".