Quote:
Originally Posted by trebuchet03
Why would a portable GPS automatically be less accurate? The math involved in GPS triangulation isn't all that complicated and in all likelihood, the GPS modules in in-dash variants (technically, mobile  ) are similar if not exactly the same.
That being said... And answering the OP. I had three GPS's running in my car at one point. One was over cell, one was for navigation used for geocaching (didn't have road maps etc.) and the third was a Magellan 3xxx. Everything was dead to nuts equal and matched with the SG  My speedometer, on the other hand, is 5mph slow at 70mph  |
The portable GPS units are less accurate because they don't use the speed sense signal from the vehicle in their calculations like the in-dash ones do. Combining the actual speed sense signal with the GPS triangulation, makes them more accurate.