The principal items of expense outside of the bank which must be figured upon are exchange or collection charges to other banks and interest paid to other banks and to depositors. If the banker is obliged to rediscount - that is to say, to borrow from other institutions - the cost of such operations must, of course, also be reckoned in. But supposing that the banker is self-dependent, the two items already named are the principal ones for which he must provide. In looking over the profitableness of an account, therefore, he first ascertains the internal cost of carrying it along, and then, so far as practicable, assigns his external costs to the accounts which give rise to them. This gives him a fair working notion of the advantage or disadvantage involved in the particular class of business, or in the particular customer's trade. He is then able to apply such corrective measures in those cases where loss is being incurred as he may think fit. Unfortunately, it is a fact that in a large number of smaller and medium-sized institutions cost analysis of the kind briefly outlined in this chapter is not very carefully undertaken. Many banks tend to work by a sort of "rule-of-thumb" method, and to make up on one item of business what they lose on another, being satisfied to take the general run of things as it goes and "average up."