I
guess it could be to do with how the average speed, and displayed speed are calculated?
Educated guess says that the speedo 'updates' every (say) half second.
And it works out the speed by taking the number of wheel revolutions in that half second.
I ought to sit down with a calculator and work out how many times the wheel goes round in half a second at 70mph, but I'm going out on a limb and saying that it will be something point 19562542983 (or some other equally non exact number
)
However, to get average speed over (say) 20 mins, the rounding from above will be much less pronounced.
Oh booger it - my OCD is reaching for the calculator...
