On 13/02/2019 19:19, Harry Bloomfield wrote:
Robin has brought this to us :
I find it hard to see how a simple count of pulses can deliver 1 per
cent accuracy.

My does around 50 pulses per revolution of the wheel, there are
electronic methods to predict the likely next pulse period and predict
when the next pulse will arrive. I have three speed displays available
to me - the dial on the dash, which reads a few percent high, digital
display which does not interpret the wheel pulses at all, it just
displays the value and entirely independently - satnav. The latter two
always agree within 1mph at a steady speed.

Only trust the satnav speed when on a level road. The speed is
calculated by rate of change of position on a flat surface. If you are
going up or down a hill it will under read.

The derivation of altitude via GPS is not very accurate anyway and is
ignored in domestic satnav devices.