[Roadsters] GPS speedo calibration

[Ronnie Day]

> So, how accurate is a GPS at displaying actual speed? I calibrated my
> roadster speedo to my GPS & it showed I was consistently at least 5 mph
> below at low speeds & 8-10mph below at highway speeds.
>
There's some lag as you speed up and slow down, but I'd run my car to
desired indicated speed on the GPS readout, hold it for a few seconds
until the speed readout settled down and then note the gear, RPM and
speed.

FWIW, I use M$ Streets & Trips 2009 with the USB GPS module on a
MacBook. I think it was around $70 at either Amazon or Buy.com. You
can usually get the software by itself for around $30. Very useful
tool for both what we're discussing as well as trip planning, etc, and
the display's a heck of a lot easier to read for us old farts. Then
again, a suction holder on the windshield doesn't work so well. <grin>

Ron