Here the calipers are seen measuring the width of the RCX. The LCD reads 16, which is a value in half-stud units. Studs are, of course, the only true unit of measure in the Lego universe.
This creation doesn't exactly need a program - just put an input into rotation sensor mode, and press the View button to watch the value.
More photos of the Calipers:
Copyright © 1999 Ben Williamson