IVS calibration - vertical?

[The North Face]

I’m reading the IVS calibration guide over at IVS/Global Setup - Dahua Wiki and there’s one thing I don’t understand in the instructions.

After calibrating the vertical reference lines, you’re supposed to calibrate the horizontal one (with “weight verification”, as it happens). In the guide example, the horizontal line gets a calibration measurement output of 1.57 meters when it’s supposed to be 1.00 meters. The guide then says

Horizontal Rule should be redrawn until closer to 1 meter when using, "Calibration Validation"

and

In the case of a major difference between the estimated value and the actual one, fine-tune or reset the parameters until the error requirement is met

What does that mean exactly? Should the line be drawn over and over until the camera gives a correct estimation? And what parameters are you supposed to fine-tune?