Like I thought, the text object isn't big enough to display the actual number "3.6000000000002" as zenox showed.
Computers cannot do fractional calculations with infinite precision, because that would require infinite computing power, so there are always small errors. Try setting the text object to:
round(Speed * 10) / 10
to only display one decimal place. In the next build I'll add some degree of rounding in the text object itself so this doesn't happen.