T E C H N I C A L D A T A of the Mechanical Calculator COMPTOMETER ************************************************************************ Model >> H << Serial Number(s): 240193 (= Outside) 38758 (= Inside) Dimensions: (ca.) Width = 10_3/4" / 27 cm Depth = 15 " / 38 cm Height = 6 " / 15 cm Weight: (ca.) 21 lbs / 9.6 kg Mechanics: 10*9 Full-Keyboard, COMPTOMETER-Coding = Instant Additions Functions: Addition, Subtraction (& Multiply & Divide) with "Tricks" Registers: Input = 10 Decimals Arithmetic = 11 Decimals Manufacturer: Felt & Tarrant Mfg.Co. Chicago, Ill. / USA 1925 HISTORICAL REMARKS ****************** The COMPTOMETER was one of the first mass-produced ADDING machines. The 1st patent was issued in July 1887. It was considered easy-to-use - but the subtraction procedure seems strange for us now. The "Owner's Manual" claims it can "Multiplication & Division" too, but the procedures are complicated. Nevertheless, it was a useful tool for the times. Because the figures of a number can be entered simultaniously, the COMPTOMETER was QUICKER THAN a "modern" 10-KEY-ADDING MACHINE of the 70s ! Citation of a book "Calculator Course" (USA, 1942) -------------------------------------------------- The key-driven calculator, such as the COMPTOMETER, is recognized as one of the essential office machines upon which modern business depends ... ... and ... is used to perform fundamental arithmetic computations with speed, accuracy, and efficiency ... BASICS & HOW TO USE the COMPTOMETER ************************************** (A) Clearing Register & Entering Data: -------------------------------------- Pull the CRANK and release it. There are three "Sensations" that occur when a new calculation is starting: o SEE: The display shows the row of ZEROS 000...00 HALF COVERED. o FEEL: The 1st KEY pressed feels HARDER. o HEAR: A bell is CHIMING. (B) Error Corrections: ---------------------- If a key is not fully depressed, the COMPTOMETER will lock. To unlock the machine, press the RED CORRECTION KEY and re-enter the figure. (C) Decimal Markers: -------------------- There are 10 small turnable arrows located above the display to indicate decimal points. ADDITION: ========= Addition is performed automatically as soon as a number is entered. Use the LARGE FIGURES on each key when entering a number! Example: 123 + 45 + 6 + 789 = 963 -------- Enter the first number 123 into keyboard. Then enter the second number 45 and notice that the intermediate sum 168 is displayed. Next enter 6 and 789 and read the result 963 on display. Remark: ------- The "Owner's Manual" suggest to use only the lower-half of the keyboard to speed-up additions (in saving hand/arm motions) according this table: instead key 6 press 3 + 3 in sequence 7 3 + 4 8 4 + 4 9 4 + 5 Obviously the method was used, because the lower-half of the keys show more wear on most COMPTOMETERs. SUBTRACTION: ============ Addition is the only operation directly performed on the COMPTOMETER. For subtraction an indirect method of addition is adopted. The keyboard contains LARGE and a SMALL FIGURES on each key. The small figures are the machine complements of the large figures: (Main-)LARGE figures = 1 2 3 4 5 6 7 8 9 SMALL figures = 8 7 6 5 4 3 2 1 0 Note: There is NO LARGE 0 and NO SMALL 9 on the keyboard! ----- Example (1): 876 - 543 = 333 ------------ Use the LARGE FIGURES on the keyboard to enter the pos. number 876. Push the small (silver) subtraction cut-out lever, located to the left of the column containing the first figure of the subtrahend (5) and hold it. Use the SMALL FIGURES on each key to enter the negative number MINUS 1 (enter 543 - 1 = 542 ) into keyboard. Release the cut-out lever and read the result 333 on display. NOTE to the following EXAMPLES: ------------------------------- Enter the positive number (in LARGE FIGURES) first ... Example (2): 765 - 493 = 272 ------------ When 9 APPEARS INSIDE THE SUBTRAHEND, no key is pressed in the column in which it appears, because there is NO SMALL 9 KEY! Push and hold the cut-out lever left of the 3rd column. Press the SMALL 4 KEY for 400, NO KEY for 90 and the SMALL 2 KEY (for 493 - 1 = 492 ). Release the cut-out lever and read the result 272 on display. Example (3): 987 - 965 = 22 ------------ When 9 APPEARS AS THE FIRST FIGURE IN THE SUBTRAHEND, the column should be treated as if it were used even though no key is to press! Push and hold the cut-out lever left of the 3rd column. Press NO KEY for 900, the SMALL 6 KEY for 60 and the SMALL 4 KEY (for 965 - 1 = 964 ). Release the cut-out lever and read the result 22 on display. Example (4): 456 - 78 = 378 ------------ When THE SUBTRAHEND HAS FEWER DIGITS, place a zero at the beginning in the column in which something would be borrowed - as if the problem were being done by the paper-and-pencil method. Push and hold the cut-out lever in the column to the left of the zero. Press the SMALL 0 KEY for the zero, and the SMALL figure KEYS for the amount of the subtrahend MINUS 1. Release the cut-out lever. Example (5): 654 - 302 = 352 ------------ When A ZERO APPEARS INSIDE THE SUBTRAHEND, the procedure is the same as in example (1), but be aware, that THERE ARE SMALL 0 KEYS! Example (6): 7654 - 3200 = 4454 ------------ When SUBTRAHEND ENDS WITH ZERO(S), "MINUS 1" refers to the last non-zero digit: Enter the subtrahend as 31__ in SMALL figure KEYS. Because: 3200 - 1 = 3199 and there are no small 9 keys, ignor the zeros! Multiplication ============== with a COMPTOMETER can be performed as repeated additions in a modified paper-and-pencil method - using the same finger-positions and hit the keys in rhythm more times ... Example: 654 * 32 = 20928 --------------------------------------- 654 + 654 <<== 2 times + 654 + 654 + 654 <<== 3 times -------------------------- = 20928 ===== Division ======== with a COMPTOMETER could be performed as repeated subtractions in a modified paper-and-pencil method - but be aware of "MINUS 1" !!! ... Example: 22 : 7 = 3.14 Remainder 2 --------------------------------------------- 22 - 7 ---- 15 - 7 ---- 8 - 7 <<== 3 times ---- 1 (Remainder 1), Dividend exhausted, set DECIMAL POINT, pull down ZEROs 10 - 7 <<== 1 times ---- 3 (Remainder 3), pull down 0 30 - 7 ---- 23 - 7 ---- 16 - 7 ---- 9 - 7 <<== 4 times ---- 2 impressum: ************************************************************************ © C.HAMANN http://public.beuth-hochschule.de/~hamann 10/18/06 |