Hello,
I know that 400mm is the bar length. The thing is that in the targets you provide the bar length of an A4 paper is 100mm, 141.4mm for an A3, 200mm for an A2, 282mm for an A1 and finally 400mm for an A0.
That’s why I think and assumed that you are using A0’s in the calibration step by step sample of the documentation.
Regards.