By the way, "Classes" is a statistical term ued in situations like defining bar graphs. Its a set of occurences between a high and low limit.

For example, a bargraph on human heigh to age may be broken down to age classes of ten years. Someone 58 years old would be in the class 50-59 years old.

In the speedometer design... the classes are the defined display possibilities, 00-99kmph. Instead of mathematically computing the precise kmph of X, your merely use a binary search to quickly find out which of the possilble display classes it fits into.

Since everything is precalculated, there is no reason to bothr calculating with the timer count X. Just compute the data table to be based upon values of X for each class. Then you just grab the count, find its speed/display class, update the display.

Actually you may want to average out the display so that you don't get a blurring display as the wheel turns many times a second near the edge of two classes. This would look like a digit displaying a 3 and a 4 in the same digit when the speed is near the class limits. An easy trick is to merely update the display every one to two seconds. That is fine for bicycle speedometers. :)

-Jay C. Box