Static pressure does not mean much in terms of sufficient charging. You need to engage the compressor and see what the pressures do in relationship to temperatures at the evaporator and condenser.

Also, once you get any liquid in the system , the static pressure will remain the same all the way up to the point you have the entire system filled with liquid.

There is a chart that tracks temperature Vs pressure for R12 and other refrigerants. AC pressure gauges will have this built into the scale.