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.