Interrupt on change is more efficient. But this is Koert's first post and he just joined, he hasn't given any indication to his level of PBP expertise..

Assuming he is a beginner, he's better off trying logic instead of interrupts to get the ball started, then switch to interrupts later as a challenge.

Koert, search for Darrel Taylor's Instant Interrupts in FAQ section. Unless you only do super simple programming, they help A LOT when using USB, timers, interrupts, and many more features.

Robert