How to precisely calibrate your LiPo Charger?

(reupload, corrected some errors)
I think most of the FPV community does not calibrate their LiPo Chargers at all. And the ones that do, they most likely use a standard DMM (digital multimeter) as a reference. In this video you will learn that normal DMMs may be too inaccurate for calibration because of the lot of different tolerances they have. Another important point is the voltage you calibrate. Because the chargers have different tolerances depending on the actual voltage they measure. You may calibrate at 3.85V and if the voltage reading is spot on there, it may be very wrong at the 4.20V top end where it is most important to end the charging to protect the LiPo cells from getting damaged.
In this video I will show how wrong the readings of usual DMMs are and I will present a different approach for calibration using a very precise voltage reference that is freely available on the market and can be easy used to calibrate your charger near the 4.20V charging limit. Much more accurate than any DMM can do.
Link to the LM4040 breakout board:
www.adafruit.com/product/2200
Music: Artlist.io