9.1 Shift differential pay, for the purpose of this Section, is defined as pay at a rate which is one step above the employee‘s base pay in the salary range for their class. If the base pay is at the top step, shift differential pay shall be computed at one step above such base pay.

9.2 Employees shall be paid shift differential for all hours so worked between the hours of 6:00 p.m. and 6:00 a.m.