Seniority for a Casual Nurse. (a) Seniority for a Casual Nurse commences on the date of the first shift worked as a Casual Nurse in the Bargaining Unit effective the date of signing and shall operate on a Bargaining Unit wide basis unless otherwise specified in the Collective Agreement. Seniority for a Casual Nurse (including a Casual Nurse in a Temporary Position) is defined as the total of hours paid to the Casual Nurse. A record of hours paid to a Casual Nurse shall be kept by the Employer and shall constitute the Seniority list for Casual Nurses.