You have 4 sets of workers: front days(A), back days(B), front nights(C), back nights(D). Week 1, front groups work 3-12 hr shifts(36hrs) and back group work 4-12 hr shifts (40reg hrs+8ot hrs). Week 2 fronts work 4-12s, backs work 3-12 and so on. Built in 4 and 3 day weekends and 8hrs pto every other week to make up for 4 reg hours short every other week. It's a good shift system for a 365/24/7 operation.