In general, you need:
1. A table where employees are listed (e.g. tblEmployees: EmployeeID, Forename, LastName, [FullName], UnitID, ...);
2. A table for employees or units payrates history (e.g. tblUnitPayrates: UnitID, Payrate, ValidFrom;
3. A payroll table (e.g. tblPayrolls: PayDate, EmployeeID, [UnitID], Payrate, ...)

FullName in tblEmployees is calculated from ForeName and LastName.

In tblPayrolls, you enter pay date for every employee and select employee ID's (or employees full names). Unit ID's (when you want to have them - it will be easier to calculate other columns when having Unit ID available) and payrates depending on pay date are calculated.

When you need e.g. unit name in payroll table too, then you need a table e.g. tUnits: UnitID, UnitName.

Btw, instead of selecting EmployeeID, you can select FullName (and calculate EmployeeID and/or UnitID, when you need them).

When employees may move from one unit to another sometimes, all goes more complex - you need a table for employee movements, and the unit info must be calculated depending on paydate.