(d) If the operating expense decreases at a less rate than does the productive output, then these tell─tale percentages automatically increase also, which the manager is quick to note, and mean a falling─off in the economy with which the plant is being operated, for increased expense means increased cost of production. This means, then, in order to be in complete control of his plant, a manager must have production costs and operating expense well in hand, for these two factors are the keys to successful management. It is up to the accountant to show the manager, in figures, the facts as to the true conditions in the shops, and the statement presented to him monthly must be sufficiently explicit to show him at short notice what the expense of operating each department of his plant has been, and what the items were that made it up. =32. Comparative Figures.= It is quite unnecessary to demonstrate the value of comparative statements, for this is generally admitted without argument. They portray at once whether what now is, shows an improvement or a falling short over what has been; in fact the degree of success or failure in any line is gauged by comparison with results previously attained. A statement showing operating conditions with those of a previous period cannot help being interesting as well as instructive; in fact it is from this source that a manager obtains the information which enables him to size up the changing conditions in his plant, and in case of loss in efficiency, shows him where the remedy should be applied. If a comparison or test is made between the operating expense and productive output, covering a period of, say, six months or a year for each department or process in the plant, as well as for the general expense, the resulting percentages show what the factory conditions will average in the long run. Any departure or deviation from this average in any succeeding month, as shown by the operating statement, serves to indicate to the manager what he may expect as the results of the present period when actual figures are in hand and actual results known. If a falling off in efficiency is noted, opportunity is offered to make economies before it is too late, and for the balance of the period to make a better showing. While it is true that an extraordinary expense, such as a breakdown of machinery, may cause an unfavorable showing for a particular month, it is quite essential that this long run average should be closely followed, in order to show that the previous efficiency has again been maintained, or better still, improved upon. [Illustration: AIR─COMPRESSOR ERECTING ROOM, CLAREMONT, N. H., FACTORY, SULLIVAN MACHINERY CO.]