I wasn’t sure I caused a chain skip when initially extending the chains, so I manually counted them off, to make sure. If you initially extended the links to 1651, divide by 6.35 to determine how many links to count off. 1651/6.35 = 260 links.
So to mark off in groups of ten, I count the outer links in groupings of 5, threading a string through, then you can mark off with a marker every ten if you like, then mark the final hole at 260.
Edit: In WebControl Actions->Calibration/Setup->Check for Chain Skip moves the chains out to the initial extend chain position, so all you have to do is put a drop of paint on the top most sprocket tooth, and corresponding chain link.