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Soemtron ETR 220 Desktop Calculator


Soemtron ETR-220
Photo Courtesy Serge Devidts, Calcuseum

The Soemtron ETR (Elektronischer TischRechner, e.g., Electronic Table Calculator) 220 is the first mass-production electronic calculator produced in East Germany (German Democratic Republic), produced by VEB Büromaschinenwerk Sömmerda. The calculator began production in 1966 through 1977; an extremely long production lifetime. Over 150,000 of the machines were produced, with minor variances introduced during production. The Soemtron ETR 220 was first distributed throughout West Germany, but eventually distribution was across many Soviet-bloc countries.

The ETR 220 is a four-function machine, with fifteen digits of capacity. It utilizes fixed decimal point logic, with a rotary dial on the keyboard panel providing the decimal point setting. The dial provides settings for 14, 12, 11, 10, 9, 6, 4, 3, 2, 1 and no digits behind the decimal point. The display uses Nixie tubes with the digits zero through nine, with no decimal point included in the tube. Decimal point is indicated in the display by small neon tubes situated between the Nixie tube display elements. The calculator utilizes discrete Germanium transistor technology for flip-flops and inverters, and diodes for logic gates. A magnetic core array is utilized for storage of the three working registers of the calculator, and three accumulator-type memory registers. The core array is unusual in that a total of seven wires are threaded through each core, as opposed to the usual four (X/Y/Sense/Inhibit) used in most core arrays in calculator applications.

The ETR-220 is functionally, and similar in many ways to the West German-made Olympia RAE 4/30-3, which was marketed in the United States by Monroe Calculating Machine Co., as the Monroe 770. It isn't certain, but it seems possible that the design for the Soemtron ETR-200 was an East-German "copy" of the Olympia RAE 4/30-3 possibly created from documentation spirited across the wall dividing East and West Germany.

Addition and subtraction typically complete within 5 milliseconds(0.005 second), with multiplication and division averaging 0.5 second. The machine operates at a primary clock rate of 25KHz. The Soemtron ETR-220 was also sold under the Daro name as shown on the machine pictured above.
Copyright ©1997-2019, Rick Bensene.