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A dummy load that maintains CC and precisely times the drop from your definition of 100% Full SoC, down to your definition of 0%

gives you an apples to apples actual mAh capacity rating.

Assuming they all started off the same, % of original actual mAh is your SoH, State of Health.

Could rig the same with resistors or light bulbs, but then precise accuracy depends on your EE skillz.

Wattmeter / coulomb counter is less accurate but good enough for many.

A 0.5C discharge rate means under 30min per cell, but gives a lower result than 0.1C

If you run multiple testers at once, cross-reference calibrate so they all return parallel results.

Also standardize temperature.

ESIR is another good tool, but much harder to standardize, IMO only use as supplementary to SoH.
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