My bad, I said refrigerant and oil in one can, was a brain fart, meant to say refrigerant and gauge in one can.

You leave the can on long enough for the system to run as cold as it will get with fans running full blast, and you watch the gauge, the gauge stays the same at the max top pressure, you quickly blast the can, let go of the trigger and watch the gauge.

It does not fluctuate drastically and is really easy to use.
I have had great success with it and I actually learned about it from another small shop that has had plenty of success with the product.

I like it, have had great success with it.
Good product.