The number of shifts is used to describe the time that is used per day in the lead time calculation (order placement), as well as the capacity that will appear in the loading plan. This is used as a "permanent value" when you use several shifts on a machine.
If the number of shifts should be described in calendar time (i.e. if during a certain period you will be using 2 shifts), you can set the Shifts here to 1 and enter the number of Shifts in the production calendar instead.
To obtain the time used per day, you multiply Basic time with the number of Shifts and any factors that were entered in the calendar. Please read more under Basic Time for additional information.