Red Knob on Laser

Hi,
What is the purpose of the red knob (in between a + and -) on the LCD display?

We had a child turn it and we don't know what it does.

Thanks,

The red knob you are referring to is an air regulator for an optional air-assist system. You do not have this air-assist system, so that knob has no effect for you.

Thanks....good to know