COMPTOMETER, compt-onee-ter (from Fr. compter, to count + Gr. meter, a measure), an adding and calculating machine, on which can be performed rapidly and accurately all arithmetical problems involving addition, multi plication, division and subtraction. The name was coined by Dorr E. Felt, inventor of the machine, in 1885. The comptometer is now widely used on all forms of figure work in all lines of business in the United States and throughout the world. It differs from all the earlier constructive efforts directed to the pro duction of mechanical calculating devices in that it was the first successful multiple-order machine to be wholly operated by the rapid depression of keys, an advantageous feature as a time-saving factor. Illustrative of the fun damental principle of direct key operation and its simplicity in practice are the following brief descriptions of how the results are obtained.
Addition is performed by merely depressing the keys according to the numbers to be added. The item 346, for example, is added by striking the 3-key in the third or hundredths column, the 4-key in the second or tens column and the 6-key in the first or unit column, and the answer ap pears in the register. Subsequent items are added in the same manner, the accumulated total being shown in the register. To multiply, the fingers are placed on the keys representing one factor, which are struck according to the digits of the other factor. For examle, to multiply 578 by 463, place the fingers on 578 and strike three times; move one column to the left and strike six times; once more to the left and strike four times and the register shows 267,614. Each key also bears on its top a small figure which indicates the power of that key for subtracting and dividing. These operations are the converse of adding and multiplying and are lilcewise performed by simply depressing the keys, but with reference to the small figures on the keytops. The only function of the lever at the side of the machine is to zeroize or cancel the answer registered preparatory to the begin ning of a new operation. In its commercial application, the use of the comptometer extends in a practical way to all arithmetical calculations of accounting, including additions; extending and footing of invoices, inventory, payrolls, estimates; maldng engineering, astronomical and scientific calculations; in all of which, frac tions decimally expressed, are as easily handled as whole numbers. Provision for the addition of common fractions is made by inclusion in the keyboard of a special fractional column or columns. By this means fractional values are
automatically accumulated and carried forward in progressive order from the lower to the next higher denomination. To meet special require ments, such as the adding of fractional denom inations of foreign currency of various kinds, the different unit divisions of weights and measures, and special uses in the various de partments of commercial accounting, suitable combinations of fractional columns are em ployed. Thus the pounds, shillings, pence and farthings comptometer, widely used in England and other parts of the British Dominion for adding British currency, is provided with frac tional columns of 20ths, 12ths and 4ffis. In a similar manner a model with fractional columns to 12ths and 16ths serves for adding British Indian currency, consisting of rupees, annas and pies. 12 pies=1 anna, and 16 annas =1 rupee. Another model supplied with fractional columns to 40ths is used for adding funts and poods, the Russian measure of weight, in which 40 funts=1 pood. A combination designed for the use of contractors, engineers and architects has columns for 12ths and 16ths which facilitate the adding of feet, inches and fractions of inches. Fractions in 60ths are provided for adding hours and minutes; and double 60ths for adding hours, degrees, minutes and seconds in the compilation of astronomical and geo graphical data. The formation of many other combinations is possible on the comptometer.
Mechanical arithmetic, as practised on the comptometer, being universal in its scope, con stitutes in itself a complete system of mathe matics. It is, of course, based on fundamental laws of mathematics, many of which are em ployed in arithmetical operations by the mental method but utilizing others not ordinarily so used. It is none the less a distinctive and orig inal system in that it involves as many and as varied, rules as are involved in the performance of arithmetical operations by the instrumen tality of paper and pencil. The full significance of the difference between the processes em ployed in mechanical and mental arithmetic could be clearly shown only by the aid of illustrative examples too lengthy for insertion in this article. The system of applied mechani cal arithmetic, with the rules for its application to all forms of arithmetical calculations, was first originated and developed by Mr. Felt. Con sult Felt, D. E., (Applied Mechanical Arithme tic' (Chicago 1895).