Two painters and then the owner.Probably IMO it's more the person using the cup than the cup itself.
If you saw the headaches I went through years ago, trying to figure what chemical was causing all my batches to fail to test, you would understand it can happen, and it does.
10% off, you would not know the difference and all the cups, depending on the section you use, are off some.
A spec for gel on a clear and a fast activator might be 55-65
Or another 330-345.
The tin does not change in grams, but this is why we have three people do the test.