Hey, for 21 yrs I have heard to charge an R-22 system to 30 deg above ambient temperature on the dishcharge gauge, guess what it did work on the old systems (I use superheat or manufacturers charging chart) and after charging a system sometimes it would match up. But now you get into the high efficiency systems and there not even close sometimes, I remove refrigerant from systems all the time to get the superheat. So the moral of the story is learn the proper way now and it will save you and customers alot of compressor failures. You will be amazed how fast you will get used to it, and you will never hook up to a system without checking the superheat and subcooling. It will make you a better technician.