Elektronika C3-15

The pocket calculator "Elektronika C3-15" is designed to solve complex engineering and scientific calculations. This machine shares the honours with the B3-18 of being the first pocket Soviet scientific calculator. By comparison, the first Western machine with similar capability was the Hewlett Packard HP-35, introduced in 1972.

The C3-15 was manufactured by the Svetlana company. A discussion of the meaning of Svetlana can be found at the bottom of the Red Calculators page. This calculator relies on ten digit positive and negative decimal numbers in scientific notation. Two digits are especially designed to store the number exponent. The numbers can be entered in scientific notation, with floating point and in mixed form. Each member of the XXV congress of the CPSU (1976?) was presented with a C3-15 calculator. The manual was provided in four languages (Russian, English, German, Spanish).

The manual for Sergei's machine proclaims "The Electronics Instruments making Union, Svetlana, is a two-time winner of the Leningrad Order of Lenin and a two-time winner of the Order of the Red Banner of Labour.

There are several variants of this machine, differentiated by operational characteristics and by some cosmetics. The C3-15 has 2 memory registers. The display is constructed of 3 groups of 5 LED digits. Whilst computing, on some machines the display blanks whilst on others the display shows blinking numbers (indicating the display register is internally used as a part of the calculation process). Numbers are displayed in mantissa + exponent form (eg: 1 is 1; 10 is 1e1; 0.1 is 1e-01), using 10 digits + decimal. The decimal point occupies a digit of the display area. After turning on power, on the display show all decimals, and C key must be pressed to clear it. Low battery is right 5 decimals.

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Type 3 variant.

The LED display is built up of 3 display units each holding 5 LED digits. There is a slightly larger gap between each of the units than between the digits in a unit, and so the display appears grouped in 5-digit segments. There are 15 available LED digit positions. Entry of numbers is limited to 10 digits plus decimal. Thus, a sign, 10 digits entered, decimal, 2 digits mantissa and sign of mantissa use all 15 available LED segments. (1 + 10 + comma + 1 + 2 = 15 segments).

A fascinating function on this calculator is the /P/ absolute sqrt(x² + y²) function, not found on western calculators. Although I have been able to enter decimal digits, all calculations seem to round to the significant decimal places (I need to re-check this; Sergei's machines don't appear to do this!). The number of displayed places is initially 2 decimals, but may be changed by pressing ARC . n where n is 0 to 9. The display will be rounded at the next calculation. The instructions are on the backplate. This is quite a slow machine; calculation of Sin(x) takes approximately 3 seconds, during which time the display blanks on some machines, and shows random garbage on others.