How to measure the recovery rate of a recovery machine ?

Hi guys,
I have a recovery station that takes a long time to aspirate. Is there a (simple or not) method to measure the recovery rate ?

Sincerely yours.

Time and weight change.

Yes, of course, I do a calculation...
I would like to prove the flow, but at the workshop, so without necessarily pump the refrigerant.
Do you know a method without connecting to a system?

Check with unit design data.