nez dans le guidon wrote:tim-b wrote:Hi
Worst case accuracy of the GPS signal is 7.8m, but this is in space. Atmospheric and other effects at bike level change this.
Military systems make an ionospheric correction for greater accuracy.
@OP crosswind, maybe?
I have a gps which runs more or less full time on my boat. It's a quality garmin unit with a garmin external antenna. It's accurate as you say most of the time but every now and then will give fixes up to 1/4 mile away. I know because it turns up in the record. That's why sailors consider gps an aid to navigation rather than a report of their position. Fit your bike with a depth sounder and radar while using the latest charts for optimal accuracy.
Some years ago we were off Brighton (making our way back to the Hamble) and our Furuno GPS with external antenna put us down in the middle of France!! Stayed like that for a few hours and then put us back in the Channel in our correct location. We switched the thing off/reset it but it was convinced we were in central France. Might have been a GPS "glitch" or maybe a problem with the system. Not dangerous (for us) because, as you say, it is an "aid to navigation".