Evening folks
After seeing much discussion about the accuracy (or not) of our beloved satellite navigation systems, I thought I would try to clarify things.
The speed seen on the screen is a “point to point” time/distance calculation which happens on a continuous basis (about every 5 metres). This works out the height change and horizontal distance and gives us a speed value. So at 80 kmh this is calculated around 250 times a minute…
This means going up or down hill will not make any difference to the reading. What you see on the screen is your actual speed over the ground and not relative to the surface of the earth.
Standard accuracy is around 3 metres best case, and this can be screwed by trees and other stuff.
The World time displayed is controlled by a ground station somewhere in Europe (shhh, can’t tell you where) and the satellites are updated from planet earth when there is a difference between ground time and space time. The stuff up there drifts (looses or gains) over a period and needs to be brought back on line.
Hope this helps
Paul