Thanks, Wastrel. Ah, yes, I was thinking along those lines. Let's stick with layer angle for the moment, for simplicity.
I wanted to get it so the player could rotate the level by pressing left or right. So I set it so that every tick, plus left is held down, the layer angle = current layer angle - 1.
Unfortinately this didn't seem to work - it would only adjust the angle by 1 degree, not keep adjusting it by 1 degree every tick if left was held down.
So still stumped!