No, more like lets use simple clock example.

Let say start time is 20:00 on 24 hour clock, and you need to add 5 hours to that, but you wish to have wrap around math, so with normal math you state 20:00 + 5:00 = 25:00, but that does not make sense on clock. With modular math, you would say 20:00 + 5:00 mod 24 = 1:00, meaning if you start at 8pm, and you need to add 5 hours to it, you would finish at 1am. In Excel the formula would be =mod(Start + End, 24).

This used in aviation to work out degrees and the like.

I will look at chapter you state and see if that give me a clue

*Edited: 14 Aug 2007, 5:35 p.m. *