M4: Calibration fail observations, large portrait vertical

OK, we may have a breakthrough.

@ronlawrence3 and @Frank_Wiebenga would you guys both be willing to give

A try?

Basically just press Retract All → Extend All then 1,000mm of belt (measured by the white part showing, length is 0 when fully retracted) will extend and can you measure that belt with a tape measure?

It will be slightly more than 1,000mm because of a little overshoot but it should be like 1009 or something like that.