The temperature would have to be what the system is at. If your air temp has been constant for a few hours and the engine is cold then the air temp should be close to what the system temp is. You would see the same pressure even with a system under charged or overcharged. (a few oz to 5 lbs of R12).
Note the middle red scale (R12 scale) that shows your system must be at 60 deg. F. The gauge accuracy is not perfect so your pretty close. Yes both sides should read the same after the system has bee off a while.