Power Monitor calibration formula

Hey all

I’m working on a new quadcopter. It’s using a 12s Li Ion pack rated at 28Ah. I flew the battery till the ground station read 24Ah used. I charged the pack, and the charger only reads 19Ah put back into the pack. What’s the best formula to use, and which parameters should I change to get accurate current readouts from my power module? I’m using an mRo Power Zero, which has been quite accurate on all my 6s builds when I compare used mAh to charged mAh.

New Amps/Volt=(Old Amps/Volt * Charged mah)/Logged mah