Q: I’m curious about the rationale behind shift differentials counting toward a WG employee’s basic pay and high-3, but it doesn’t count for GS employees. Why is this? Is this an OPM regulation? Is there a way I can learn more about what I see as an inequity to GS employees because shift differential doesn’t count toward their high-3? A: Shift differentials for wage-system employees are provided for in law. Such a provision isn’t needed for general-schedule employees because these and other factors are included when determining their job grades.