The present worth of a machine is the difference between its first cost and the present value of the sinking fund. If _m_ represents the present age of a plant in years, then the present worth is _P_ = _C_(1 – ((1 + _r_)^n − 1)⁄((1 + _r_)^m − 1)). TABLE 32 COMPARISON OF COSTS OF THREE DIFFERENT PUMPING STATIONS. NOMINAL CAPACITY THIRTY MILLION GALLONS PER DAY RAISED THIRTY FEET ────────────────┬────────────────────────────────── Equipment │ Plant A ────────────────┼────────────────────────────────── │One Acre of Land. Brick Building, │ Steel Trussed Roof, Slate │ Covered. Cross Compound │ Condensing Horizontal Pumping │ Engine ────────────────┼───────┬──────────┬───────┬─────── │Annual │ Years of │Sinking│ Total │Payment│Usefulness│ Fund │ │ on │ │Payment│ │ First │ │ │ │ Cost │ │ │ ────────────────┼───────┼──────────┼───────┼─────── Land │ 100│ │ 0│ 100 Permanent │ 1188│ 50│ 1080│ 2,260 Structures[49]│ │ │ │ Pumps and │ 440│ 15│ 435│ 875 Machinery │ │ │ │ Boilers │ 280│ 10│ 446│ 726 Labor │ │ │ │ 14,000 Fuel │ │ │ │ 5,500 Repairs, etc. │ │ │ │ 480 ────────────────┼───────┼──────────┼───────┼─────── Total │ │ │ │ 23,941 ────────────────┴───────┴──────────┴───────┴───────