Argon gas flow regulator accuracy

I started to question the accuracy of the gas flow regulator after have difficulty getting "shinny" Al weld beads and getting filler rod oxidation unless I was able to maintain a perfect technique.

Being inexperienced I have adhered to recommended gas flow rate of 2 to 2.5 times cup size. I have shied away from turning up the gas flow for fear of turbulence sucking atmospheric O2 into the gas flow.

I purchased a $6 flow tester/meter. to determine exactly what I am getting out the cup. (https://www.amazon.com/dp/B06XW8H8W1...fed_asin_title)

Measured various SCFH regulator settings and below are the results:

Attachment 14241

Note: PowerTIG 210EXT, 25ft WP-9 torch, #6 cup (no gas lens)

Two things surprised me: 1) how nonlinear the results were and 2) the amount of discrepancy between the regulator and flow test meter.

Checked the line connections for leaks going into the back of the welder. Did find one minuscule leak and corrected it.

Has anyone checked the gas flow out the cup relative to what the regulator is set to and observed something similar?

I wonder how much the 25' torch cable length contributes to this behavior.

Note: For some reason my machine shipped with 25' torch cables instead of 12.5' ones.