Or, again, if it is desired to obtain not only such in dividual costs but also the summarized costs of the propelling machinery, such summaries are a necessity. In the example shown, Figure 23, the factory expense is computed separately, as would be necessary if dif ferent percentages were used in different departments: The general and selling expense is also computed and added, and in this way the total factory cost is ob tained.
11. Comparative recorcL9.—It will be evident that the above methods are sufficient for the purpose of re cording total costs. If, however, it is desired to use these recorded costs as a means of fixing piece rates, or estimating on contracts, it is very often desirable to express them comparatively, since a single set of costs is not likely to be reliable as a guide to future work. If costs are recorded by production-order numbers, as explained in the foregoing discussion, only the totals of the several items are quickly available.
In the case of the pump, illustrated in Figure 23, the summary will have back of it a number of sub sidiary summaries, each giving the total for one of the components of Figure 23. If these subsidiary sum maries are filed under the controlling production order number, it is obvious that more or less difficulty will be experienced in finding the comparative cost of a given piece as manufactured for different pumps of the same size and kind.
12. Costs by classes.—If, on the other hand, the cost of detail parts is recorded by classes and not by production-order numbers this difficulty is obviated. This method is illustrated in Figure 24, opposite, where the details of the manufacture of several lots of turret-lock rings for turret-lathes are thus re corded. The record given in Figure 24 is very com plete, the work being recorded by classes and also by production orders. The Ar, and H, under each class of operation, indicate whether the work has been done by a mechanic, apprentice or helper. The num ber of minutes expended on each operation for the lot is recorded and directly underneath is the cost per piece. On the right the totals of these items are sum marized, together with the total cost per piece in each lot. Records of this kind are very instructive in set ting piece rates or comparing methods of production.
13. Detail of the case of the construc tion of a single machine or of a small number of ma chines, where a repetition of the order is not prob able, it is sufficient to record the cost by production order number, filing the detail and summarized costs, which are obtained, under a few order numbers. But in manufacturing a standard product, which is in more or less continuous production, the method of filing by classes 1 is much more useful. Obviously, many variations may be made in these methods, and it should be remembered that the usefulness of the final cost record depends largely upon the intelligence with which the production orders are issued. In one case it may be sufficient to group all costs under a single order number and summary; in another it may be necessary to divide the job under a number of pro duction orders, and to carry the summarized cost of each group to a grand summary under the main order number; or, again, it may be necessary to record all costs by classes and make up the total cost of a given product from class costs. In still more complex cases the main parts of a machine may be made on a special production order, while, to complete it, many auxiliary parts may be used that have been manufactured on class-order numbers. In the last method, the draw ing list, Figure 5 (page 55), is an essential feature of the productive process.
14. Indexing cost summaries.—It is clear that in a busy factory turning out many jobs monthly the cost summary cards will increase rapidly. They should therefore be filed in some systematic manner, and if necessary should be indexed in some way so as to make reference to them quick and accurate. In many cases an alphabetical index by customers' names may be suf ficient; but in most cases filing and indexing by classes is necessary. Thus all generator costs may be filed to gether, all induction-motor costs may be filed together, and so on. In the system referred to in the footnote on page 281, the method of filing and indexing by classes is very fully worked out. Thus, in that system, all cylinder-head costs are filed together, all connect ing-rod costs are filed together, and so on Clearly a good index makes the cost records very much more effective; in fact, in large systems it is indispensable.