Bystritsa, Bystritsa-2 and the Bohn Contex machines

©Sergei Frolov

This Soviet electro-mechanical calculator, the Bystritsa-2, is capable of multiplication and (clunk-ca-clunk-clunk-ca-clunk...) division. Mechanically, its amazing they work at all. Very 'cheap' metal stampings and plastic parts (gears, no less). The strange part is that after all of these years, most of these calculators still work flawlessly today! That's a testimony to the design, which must have a lot of built-in tolerance for manufacturing and 'environmental' variation. As with many of the electronic calculators, the Soviet machine seems to be heavily copied from similar Western machines - in this case, the Bohn Contex electro-mechanical calculators, one of which (the Contex-30) is in my collection. I won't run my machine after 10pm, for fear of waking the neighbours! Timo Leipala has checked the introduction year of Contex-30, and it is either 1965 or 1966. It was not yet displayed at Hannover fair 1964 and the manual for his machine was printed 1966. For other Contex models, the exact introduction years (at least, in Scandanavia and Germany) culled from ads and Hannover fair lists: Contex-10 (hand operated): 1957 Contex-20 (electromechanic): 1961 Contex-55 (electromechanic, non-interesting, non-weird model with automatic division): 1968 The Contex-30 was still displayed at 1970 Hannover fair but no longer 1976. The 1974 date on a transistor inside Sergei's machine correlates well with the availability dates of the machines from which it was copied.

Correction Return Stop Quick-Shift Return

CONCISE INSTRUCTIONS

TO CLEAR THE REGISTER; Depress the clearance key [C]

TO CLEAR THE KEYBOARD; Push the red correction key to the extreme right

ADDITION; 722 + 421 = 1143. Enter 7-2-2 in the keyboard. Depress the plus key [+]. Enter 4-2-1 and depress the plus key [+]. The register now indicates the result.

TO CLEAR THE MACHINE; Depress the clearance key [C]

SUBTRACTION; 722 - 421 = 301. Enter 7-2-2 in the keyboard. Depress the plus key [+]. Enter 4-2-1 and depress the minus key [-]. The subtraction is over and the result can be read from register.

TO CLEAR THE MACHINE; Depress the clearance key [C]

MULTIPLICATION; 722 x 421 = 303,962. Enter one factor in the keyboard, in this case e.g. 7-2-2. Depress multiplication key [x]. The machine multiplies automatically. Enter first 1, then 2, and finally 4 in the keyboard. The multiplication is now completed and the register indicates the result 303,962.

TO CLEAR THE MACHINE; Depress the clearance key [C] and push the correction key to the extreme right

MULTIPLICATION WITH A CONSTANT MULTIPLICAND; When several multiplications are to be made, all with the same multiplicand, it is necessary, after entering of the constant multiplicand, say 125, to depress the return stop key ( ) and push it to the left until it touches the correction key \/( ). After each calculation depress the clearance key [C] and push the correction key \/ to the right until it touches the return stop key ( ). The constant multiplicand 125 remains in the machine and can now be multiplied by the next factor in the same way.

TO CLEAR THE MACHINE; Depress the return stop key ( ) and push it to the extreme right; push the correction key \/ to the extreme right, and depress the clearance key [C].

DIVISION; 625 / 25 = 25. Enter the dividend 625 in the keyboard. Depress the quick-shift key [-:-]. Depress the plus key [+]. Enter the divisor 25 in the keyboard. Depress the quick-shift key [-:-], depress the division key [DIV] and the minus key [-]. When the machine stops automatically, write down the red figure in the quotient window to the right of the register, in this case "2"; this is the first digit of the result. Depress the return key [-..]. When the machine stops automatically, write down the red figure in the quotient window - this time "5", which is the next digit of the result.

If there is a remainder, continue to depress the return key [-...] until you have the required number of decimals.

NOTICE; If, due to misoperation, the machine does not stop automatically during division, stop it by depressing the clearance key [C].

TO CLEAR THE MACHINE; Depress the clearance key [C]. Push the correction key \/ to the extreme right.

The previous generation of the Bohn Contex machines were very similar to the machine depicted here, except there was a big handle that you pressed to activate the mechanicals... people-powered Contexs. Division on these early machines works the same way, except you have to keep pressing the cycle bar repeatedly until the machine 'locks', then write down the red digit in the cycle counter window, then press the right shift key which shifts the divisor to the right one digit, and start pressing the cycle bar again. They automated the multiplication on your machine in a similar way; you enter the multiplicand and press the cycle bar, then push the X key, and cycle the machine as many times as the last digit of the multiplier, then press the <- key to shift, then cycle as many times as the next to the last digit of the multiplier, etc. until you've cycled through all of the digits of the multiplier reading from right to left.