readout

Does anyone know how often this is supposed to recalculate itself? I.e. is it set at every nth second? I've noticed that my readout on the trip computer seems to stop calculating the average speed shortly after I reset it. I.e. for the first couple of miles it will update every few seconds...

well as you know i had the car remapped by Will over a week ago... and the little bugger was smoking a little to much for my liking (the car not Will). so a trip back was on the cards. a week went by to quick and friday had come, time to see Will again. after a 4 hour run to wolves (traffic...

Is this an average or current speed?