RULE 4. ASSIGNMENTS. (a) Yardmen shall be assigned for a fixed period of time, which shall be for the same hours daily for all regular members of a crew. So far as it is practicable, assignments shall be restricted to 8 hours work. Yardmen will be given at least 16 hours advance notice when assignment is to be discontinued. Any engine working three consecutive days will be considered regularly assigned.

(b) When a regular assignment is abolished on the first shift, yardmen will be advised not later than 11:00 a.m. on the day previous to the discontinuance of that assignment.