The Overrides tab allows you to set which department will be used in calculations when the shift is applied. For example, a shift can be set to override the department to Shipping. An employee who's home department is Warehouse will have their accumulated time allocated to the Shipping department for the days that shift is applied to. If no department override is selected, all hours worked will be allocated to the employee's home department or to a department into which they transferred.
Wed 12/05/2018