The statement of a few principles of cost accounting, and the illustration of a few blanks in use should be sufficiently suggestive to lead a resourceful engineer in the right direction.[79] Costs should be divided into four general classifications: labor, materials, equipment, and overhead. Labor should be subdivided under its several different classifications arranged in accordance with rates of pay. The number of laborers under each classification and the amount of work done per day should be recorded. Fig. 86 is an example of a form which may be used for such a purpose. [Illustration: FIG. 86.—Foreman’s Daily Payroll Report. From Engineering and Contracting, 1907. ] Materials may be recorded as they are delivered on the job, as they are used, or in both cases. Measurements are usually easier to make at the time of delivery, but records made at the time materials are used are more serviceable. For example, 100 barrels of cement may be delivered on a job in November, 50 of them are used before the job freezes up and the other 50 are held over until spring. It would be misleading to charge 100 barrels used in November. Fig. 87 is a form in use for an inspector’s report on materials. The total cost must be made up in the office from these records and a knowledge of unit costs. [Illustration: FIG. 87.—Foreman’s Daily Material Report. From Engineering and Contracting, 1907. ] Equipment consists of tools, animals, machinery, and apparatus used in construction. Only equipment that is actually used should be charged to the job and a credit should be made at the completion of the job for the fair value of the equipment remaining after the completion of the work. Overhead charges include the expense of the office force, superintendence, and miscellaneous items such as insurance, rent, transportation, etc., which cannot be charged to any particular portion of the work but are equally applicable to all portions. It happens frequently that many jobs are handled in the same main office. The division of overhead becomes more difficult and is frequently arranged on an arbitrary basis, e.g., each job may be charged the proportion of overhead that its contract price bears to the total contract prices being performed under that office. This rule may be modified when it becomes evident that some job is taking distinctly more than its share of the overhead. Estimates of work done in any period can be made with the above data in hand by subtracting the total costs of the work up to the beginning of the period from the total costs up to the end of the period. Fig. 88 shows a sample blank from the final estimate sheets used at Scarsdale, N. Y.