67 Barracuda oil pressure gauge

Spinning the oil pump with a drill, then rotating the crank about 3”, then spinning the oil pump some more. I’m doing this by myself.

I can turn the key on, spin the pump, and the OP gauge is now moving. I can tell because the pressure is bleeding down when I get out from under the hood and look at the gauge.

Which leads to the question, “What do the increments on the OP gauge mean in pounds of oil pressure?