It does have index marks on it. So far, I used a bit of masking tape to mark my position. If the 145mm crankset is too short, I will likely try a 155mm one. I noticed there is a “bump” on the bottom of the cross member of the frame that the bottom of the boom hits when fully retracted. Maybe instead of cutting the boom (if it comes to that), I may just try cutting the bottom end of the boom at an angle so it goes beyond the cross member. ( =/ )