AussieJosh
Member
- :
- Mazda CX-5 GT Deisel
The speedo and GPS will always bee different if every model of vehicle.
The speed by law has to be a small percentage *below* the actual speed. Typically this could be anywhere between 95% and 99% of the actual speed.
Presently GPS is very accurate for civilian use. The speed indicated on the GPS in clear view of the sky, and without interference has a confidence level of 95% to be within 2 metres of accurate. So 112 on your GPS is most likely to be 112 in actuality.
No issue with your speed. It is completely *normal* and completely *legal*.
Just for the record, President Clinton is responsible for bringing accuracy back to the GPS signal to civilians (and hence the world). Prior to then, intentional errors were added to the civilian band. This was in part to ensure that GPS units couldn't be used to allow extremists to launch and control rockets using the device. To get around that the civilian band has a speed restriction which causes it to lose signal at the speeds that would be reached by launching rockets.
Sources:
http://www.gps.gov/systems/gps/performance/accuracy/histogram.png
http://support.radioshack.com/support_tutorials/gps/gps_SA.htm
Good info inodes, very interesting about the civilian gps band - never heard that before.