Too loose and the gear slips under load, which looks exactly like under-extrusion. Too tight and it crushes the filament oval, which also causes under-extrusion. Both get misdiagnosed as flow.
Phase 0 — Mechanicalabout 10 min
How to do it
Back the tension screw off until filament slips freely.
Tighten in small increments until it feeds without slipping.
Pull a length out and inspect: light tooth marks are correct, deep gouges or a flattened cross-section mean too tight.
How to read the result
Filament shows light, even tooth marks. It feeds by hand with moderate resistance and does not slip when the hotend is under load.
Does your printer have this?
Look at the extruder, where filament enters the hotend. You HAVE this if you can see a thumbscrew, a knurled knob, or a small arm held by a spring that you could squeeze — anything you could turn or press without tools. You DO NOT have it if the extruder is a sealed block with the filament path running through it and nothing adjustable on the outside. Many modern machines, the FlashForge Creator 5 among them, use a fixed spring preload set at the factory. If you can only see hex screws holding the housing together, those are assembly screws, not tension adjustment — do not turn them.
Redoing this invalidates
Calibration is a chain. Change this and the results below were measured against the old value: