Must I "zero out" manifold gauge set before checking pressure?

[AltimaGuy]

I have a manifold gauge set that I used to charge an empty system by weight to factory spec with a refrigerant scale. The manifold gauge set still has some refrigerant/gas in it as I just closed the valves off and hung it up when I was done.

So, do I need to vent/empty the manifold gauge set before checking pressures on this or a different car?

Does the manifold gauge set need to be reading all zeroes anytime I go to check pressure on something going forward?

[Dougflas]

Unless you use different manifolds for different refrigerants, yes clear out the gauges and zero them out for accuracy. You should not mix oils either. It is best to have a different set for different refrigerants.