Design Flex Pro shows new and used belt tension information, but how do you know a belt is "used"?
V-belts stretch more than synchronous belts. Most of that elongation occurs within an initial run-in period and V-belts should be retensioned to the “new” value. Any time the belts are retensioned after that, use the used value. Synchronous belts also experience tension decay, but not enough to require retensioning. When planning to re-install used synchronous belts, measure and record the tension before removing and reinstall at the recorded tension. If that wasn’t done, then re-install the belts at the “used” belt tension specs shown in Design IQ or Design Flex Pro.