rotary switch / turn knob? how to call it?

Im looking for a switch-like rotary knob, that i can turn left and right. Its outputs a simple 'pulse'. You find these in selecting/setting numbers on assorted electronics. You can keep turning them (both directions), there is no absolute '0' point. But i need to know, if you turn left or right.

Its for a simple Arduino project, i want this rotating know/switch to increase the number on a LCD (turning right) and decrease the number when turning left.

But whats the name ??

Thanks.

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