=123. Cost Data and Estimates.=—Cost account keeping and the making of monthly or other estimates are closely connected. Cost accounts are of value in estimating the amount of work done to date, and in making preliminary estimates of the cost of similar work. Although the engineer is not always required to keep such accounts, they are usually of sufficient value to pay for the labor of keeping them. Under some contracts the contractor’s accounts are open to examination by the engineer. Usually, however, he must depend on reports from the inspectors for information concerning the man-hours required on different pieces of work, and on his own measurements of materials used and his knowledge of their unit costs, in order to make up an estimate of total cost.
The measurement of a completed structure and a summary of the materials used in its construction may act as a check on the use of proper materials as called for in the contract. For example, if it is known that 2,000 bricks are required for the construction of a manhole and if only 15,000 have been used in the construction of ten manholes, it is probable that some or all of the manholes have been skimped. Similar conditions may show in the proportions of concrete, backfilling in tunnels, sheeting to be left in place, etc.
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.
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.