The case of an office building may now be considered, as differing as widely as possible from unimproved properties. Here the income is from "rent." As to expenditures, we have in addition to those already considered, another and quite distinct class, consisting, first, of repairs and cost of maintenance; and second, of such charges as those for engineer and janitor service, and for light, power, elevators, etc. All these expenditures are necessitated solely by the fact that certain conditions must be complied with before rents can be collected, and they are classified as the costs of maintenance and operation.

This difference, however, in no way affects the principles already laid down in discussing unimproved property, or the procedure to be followed, except that the memorandum accounts in the real estate ledger, dealing with improved property, should show the net income derived from this source.