Scale/Flowrate Calibration Cube
thingiverse
Pretty Basic Calibration Cube 20mm x 20mm x 20mm Hole is 10mm and walls are 5mm. If it measures 20x20x20 but the hole isn't 10mm, divide hole measurement by 10 then multiply that by current flowrate to get new flowrate. Not the best method out there but it works for me.
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