RULE 79. YARD WORK TRAIN SERVICE.  Work train service exclusively within the switching limits of terminals or yards where yard locomotives are assigned shall be performed by yard engineers or engineers from the extra, board. Regular yard engineers, or engineers from the extra board, who perform work train service in yards or terminals and yard switching during their shift shall be paid for the actual time consumed in work train service at work train rates with a minimum of one hour in addition to the regular yard pay and without any deduction therefrom for the time consumed in said service. Yard engineers or engineers from the extra board performing work train service exclusively will be paid work train rates for the day or tour of duty. No payment will accrue to road engineers in connection with performance of work train service by yard engineers that is exclusively within switching limits, but road engineers will be used for work train service not exclusively within switching limits.