[mrein3]

Looks like you're off by a constant 10%.
Think about it. At 40 mph, add 10% and you get 44 (your table says 43)
At 65 add 10% you get 72.5 (your table says 73).

This is why it is important to learn math. Your high school teacher was right, you really do use math every day.

For a bouncy speedo you may need to lubricate the cable. You can remove the cable from the back of the odometer, pull out the center, lubricate it, and stuff it back in there. If it gets cold where you are don't use a lube like white lithium grease - that stuff can get pretty stiff when it is cold.