Records of production, as well as records of time, are necessary for two reasons. First, when the piece rate or the more modern premium system is used, employes are paid according to the number of units produced. Second, to obtain accurate records of costs, it is necessary to have accurate records of production. For the purpose of determining the amount of wages due the piece worker, time records are not needed; records of production supply the information required. But to determine the actual labor cost per unit, time records are needed even in the case of piece workers. Piece rates are based on continuous production at a uniform rate. A marked falling off in production means a perceptible increase in the cost per unit for overhead expense. For example, we will suppose that a manufacturer has $50,000.00 invested in machines operated by piece workers. One of the definite items of expense to be apportioned to the product of these machines is interest, at say five or six per cent. If production falls to one─half of the normal quantity, because one─half of the machines are idle, the amount of this one item of expense that must be borne by each unit of production is doubled. Or, we may have two workers operating identical machines on the same class of work, the production of one being twice that of the other. The overhead expense is the same for each employe and each machine, consequently the cost of the finished product is affected by the factor of time. The piece worker who fails to maintain the rate of production established as standard in his or her trade, is not a profitable worker. =7. Time─Keeping Systems.= There are several systems or methods of time keeping in use. No one system is adapted for use under all conditions. Like all other classes of records, the time─keeping system must be selected with reference to the conditions under which it is to be operated. The system used in a factory, where all operatives are housed in one or more buildings, is not well adapted to the needs of a contractor whose men may be working on jobs located at points widely separated. In this discussion, we will consider first the systems used to record the total time employed. This will be followed with descriptions of systems for obtaining records of production. =8. Time Book and Check Systems.= Of the time─keeping systems that have been at some time considered standard, the oldest is the time book kept by the time─keeper. This system required the time─keeper to identify each man at work, and to record, opposite his name in the time book, the number of hours worked each day. Sometimes a special time─keeper was employed, or the foreman might keep the time book for his own men, the time books of all foremen being turned in for the purpose of making up the pay─roll. A system so dependent on the memory of one man never could become satisfactory.