Modulo is a mathmatic operation. -taken from the NI Reaktor user forum: http://www.nativeinstruments.de/index.php?forum_us -

The Div output is the integer part of the division, the Mod output is the remainder from the division. The mod output will always be in the range 0...[b-1] The div output will always be Int(a/b) (where "int()" mean "drop any fraction - DON"T ROUND)

16 div 3 = 5 16 mod 3 = 1

8 div 5 = 1 8 mod 5 = 3

9 div 5 = 1 9 mod 5 = 4

10 div 5 = 2 10 mod 5 = 0

5 div 8 = 0 5 mod 8 = 5