A nurse assigned by the department head or his/her representative to perform the duties of a higher level class on an acting basis shall, after five consecutive workdays, receive retroactive to the first day of such assignment, acting pay which shall be computed at one step more than the nurse’s current salary in his or her present class.  Nurses who are at the top step of their salary schedule and are otherwise eligible for acting pay in accordance with this section shall receive the equivalent of one step (5.74%).  Work assignments shall not be changed for the purpose of evading this requirement of providing acting pay to a nurse who would otherwise be eligible for such acting pay as provided herein.  Except under unusual or extenuating circumstances, the County shall offer work out of classification assignments to permanent nurses before offering them to per diem nurses.