Working at NMO, our Collins 651S-1 receivers were programmed to scan the ship calling frequencies on each band. I might have the 4 and 6 MHz receivers scanning in my left headphone, and 8 and 12 MHz in my right headphone. The other op would have 16, 22, and 26 MHz, plus the fixed freq/y of 8364 KHz. Four hours of that, then four hours at the 500 KHz position, then the final four at the HF and VHF voice position. Other positions to choose from were HF air-to-ground, and HF RTTY.
We'd work 12 hours on, 12 hours off, 12 hours on, then 72 hours off. If those three 12's were days, then the next cycle of 12's would be nights. Never really felt well rested from continually shifting between days and nights.
73,
Jeff KH6O