Calibrating Pressure Advance (Flow Dynamics) in Bambu Studio

Applies to all Bambu Lab printers. P1S and P1P owners: this is essential, because those printers can't calibrate automatically.

Steps

Import and select our Pro PCTG filament and process profiles for your printer. See How to import profiles into Bambu Studio.
Make sure the nozzle selected in Bambu Studio matches the one installed.
Clean the nozzle and make sure the filament is dry.
Open the Calibration tab, choose Flow Dynamics, then Manual Calibration. Select your nozzle, plate, and the Pro PCTG filament.
Print the test pattern. The pattern test is easier to read than the line test.
Choose the line with the cleanest corners and most even width, and save the K value to your Pro PCTG preset (and AMS slot).

Pressure advance not enabled. We've seen customers calibrate a value that never gets used. Check that it's turned on in the filament profile.
The value disappears. Bambu Studio sometimes stops showing a saved value. Restart Bambu Studio.
Running the Flow Rate test instead. Flow rate and flow dynamics are different calibrations. Flow dynamics is the one that sets pressure advance.
Transparent colors on X1-series printers. The automatic calibration can struggle to read clear filament. Use manual calibration.