This article revises and updates through 1984 an annual and quarterly series originally constructed from 1952–1968 on the average workweek of capital in manufacturing. The series provides estimates of the input of capital services into production and uses data on production-worker employment, shift patterns, and weekly working hours to estimate the number of hours that the capital stock is operated each week. The updated series indicates that the capital stock is working longer and the hours of operation are more cyclically variable than in the earlier period. Shift work is found to be an important source of variation in the hours of operation. The findings imply a change in the relationship of the capital stock to manufacturing production.