Thus far the analysis is comparatively an easy one even if the results obtained are not much more than approximate. Now, however, it is necessary to recognize that there is nothing fixed about bank expense or bank cost in so far as refers to individual transactions. This is because the volume of operations handled determines the cost per unit up to the point where it is necessary to add further elements of cost. For instance, suppose that a given staff of men in the paying teller's department can pay five thousand checks a day. Suppose, however, that the bank's clientele is not of a kind which habitually presents many checks for cashing; so that, as a matter of fact, not more than five hundred to a thousand are daily presented for payment. Inasmuch as the bank must maintain a complete and well-organized staff in that department, it would seem that the expense of handling each one of these checks is anywhere from five to ten times as great as if the staff were working at capacity. In the same way, imagine the case of an institution which is equipped and able to handle collections running into a given number of thousand items daily - say, ten thousand items. Clearly, if its depositors only bring it five thousand items daily the proportionate expense of the collection department is, relatively speaking, very high. This peculiarity of banking is the same that is to be noted in the case of public-service corporations. Suppose a street-car line is obliged to run a car over a given route at least once in five minutes. Experience shows that a car run once in ten minutes will be comfortably filled, but a more frequent operation of cars does not result in a corresponding increase of passengers, so that each car is not more than half full. Here the more frequent service is simply so much added expense. Economy in operating the bank is likewise found in adapting the size of the staff to the average volume of its items in each department - first ascertaining from experience about what customers will require, then enlarging or contracting the staff in each branch to correspond thereto. Even when this has been done, however, the variation in costs will be a very great one. Suppose, for example, that a large bank, whose customers seldom present checks for cashing, has a small staff of men in the paying teller's department. Suppose, further, that this small staff has its time fully occupied even with the limited number of checks which come through. Contrast with this bank the case of another in which a very large volume of payments is daily made and a correspondingly large staff employed. The chances are that the cost of paying a check in the bank with the large volume of payments will be very much less than in the other. This makes it difficult to hit upon any standard scale of banking costs proportionate to operation.