you have done it once you can understand what they mean. There is no visual difference in the sight glass between a correctly filled charge and an over charged condition. The key to a successful recharge is taking your time. If you do it to fast an over shoot the charge, you won't know it because you see no bubbles and think you are still low. Add smaller amounts of refrigerant in 5 to 15 second bursts, letting the system stabilize for 3 to 5 minutes. Then check the sight glass. You see some bubbles, good. Do it again. Let it stabilize. You see some bubbles, good. Do it again. Let it stabilize. Now you see smaller bubbles. Good. Do it again and let it stabilize and now it's clear and no bubbles. Your done. The key is do it slowly AND let it stabilize between 15 second bursts. As I said, don't over shoot or you could put an extra can of gas in which is not good! Hope this helps.