, then the second number is entered, and only then the required operator key is pressed. The stack in this calculator consists of three registers – X, Y and Z. This calculator was the first to accept and display numbers in floating point format (with mantissa and exponent). It used a – digit red LED display. [F] [X] In , another very powerful engineering calculator was introduced, the C3 – . This calculator had increased calculation accuracy (up to (numbers), worked with exponents up to 9. (e) , had three registers of memory, but most remarkable: worked with algebraic logic. That is, to calculate the expression 2 3 5 it was no longer necessary to calculate first 3 5, and then add 2 to the result. This expression could be written down in a “natural” way: [2] [ ] [3] [=] [*] [=]. Besides, the calculator is supported up to eight levels of brackets. This calculator, together with its desktop brother MK – 51 were the only ones having a “/ p /” key. This key was used for calculations under the formula sqrt (x ^ 2 y ^ 2) [F] [X]

In 1982, the K (IP) microprocessor was developed and it was used as the basis for a whole series of calculators. The first of them was the well known B3 – calculator (displayed on the right). Then the (B3 – M, B3 – , B3 – (M) and (B3 – A, B3 – A) calculators were crafted with identical look, just by removing some functions. [F] [X] (Based on the B3 – calculator, the B3 – (with percents), the B3 – (A) with square root) and the B3 – G (with memory) were made. By the way, priced at (roubles, the B3 – A calculator subsequently became the cheapest Soviet calculator. The B3 – (was soon named as MK – 38 and so was its brother MK – and the MK – 69 A, which had similar functions. [F] [X] Svetlana’s factory launched model C3 – , which in reality did not have success, and soon was replaced by the very popular and cheap model C3 – 40 (MK – [F] [X] One more direction in the development of microcalculators were the engineering calculators B3 – (MK – [BP] ) and B3 – (MK – 46). B3 – differed from B3 – by having a simpler design and costing five roubles less. These calculators were able to convert degrees into radians and vice versa, multiply and divide numbers in memory, and also calculate a factorial. It was very interesting the way these calculators calculated a factorial – simple sort out. The calculation of the factorial for the maximum value of took more than five seconds on the B3 – 50 calculator. [X] These calculators were very popular in the USSR, although they had, on my opinion, a defect: they displayed too few significant figures, as many as the precision guaranteed in the manual. They usually had five to six digits for transcendental functions. [X] (The desktop variant MK – was based on these calculators. By the way, many pocket engineering calculators had their desktop counterparts, for example: EPOS (A) B3 – 34), MK – (C3 – ), MKSCH-2 (B3 – 39), and MK – (B3-) , B3 – 51). [X] The calculator MKSCH -2 – became the standard “school” calculator – Except for some demonstration units, it was produced by the Soviet industry for exclusive use at schools. This calculator, as well as the non-RPN B3 – calculator (shown at the left) was able to calculate the roots of a quadratic equation and find the roots of a system of two equations with two unknown variables. On its appearance this calculator is completely identical to the B3 – calculator. [F] [X] All key inscriptions follow the western standards. For example, the key to record a number in memory was designated “STO” instead of “P” or “x -> P”. The key to recall a number from memory was designated “RCL,” and so on. [X] Despite the capability to handle numbers with large exponents, this calculator used the same eight-digit display of the B3 – 24 calculator. The developers decided to display floating point numbers with the mantissa and the exponent, leaving room only for five significant digits. To address this problem, the calculator was provided with a “CN” key. For example, if the result of a calculation was the number 1. e – , the display showed 1. – . By pressing [F] [F], the display showed . The decimal point was omitted. [F]
[F] The first Soviet programmable calculator [F] [X] The First. Soviet programmable calculator B3 – (shown at the right) was developed by the end of and sold at the beginning of 1980. It was one large step forward. Before, users had to repeat calculations many times, and calculators had a maximum of three memory registers. Now users were able to write programs and store instructions and numbers in memory. The term “programmable calculator” caused awe and some shivering of voice. It was a very expensive calculator – it cost the whole 718 roubles! Soon calculators were conferred a mark of quality. [X] (The first models of the Elektronika B3 – [max] had a red LED display. The comma used one full position in the display. Later the display was changed to green fluorescent but this made its operation slower by (%.) [X] The calculator worked with Reverse Polish Notation, this required to enter first the two numbers and then the operator. After entering the first number it was necessary to press the upward arrow key . Except for two operational registers X and Y, the calculator had a circular stack consisting of six registers. The stack of numbers was connected to the register X. Special keys allowed to move the numbers clockwise and counter-clockwise within the circular stack. In addition to the circular stack and the X and Y registers, this calculator had seven storage registers (# 2 to # 8). [X] The calculator had two operation prefix keys – “F” and “P.” The “F” key was black and the “P” key was red. Prefix keys were also used to store and recall numbers from the registers. The “P” key was used to store, while the “F” key was used to recall. [X] But But the main feature of the B3 – 33 calculator has not been mentioned yet – the ability to program! The calculator supported 70 steps of program, and the addresses were named with a module of six, therefore the addresses had the following order: 06, 09, , 12, , , , and so on. Each key had an operation code. The calculator had functions for unconditional transfer, transfer to subroutines, and also conditional branching. The branching keys used two memory locations on the calculator – one cell to store the operation code, and another to maintain the branch address. The required transfer address was equal to the code corresponding to the transfer key minus 1. For example, in order to jump to address , it was necessary to press keys [BP] and [3] (code [X^Y] ). The operation codes were taken from a table. [X] [max] Suddenly, the first programmable calculator became very popular in Russia. Now the user could not Only write complex programs, but also play games with the calculator. It was an Unprecedented innovation! Literature on engineering programming with the programmable calculator started to appear. At the left, a very popular book of those years devoted to games and other useful programs for the B3 – … [X] (The introduction of the programmable calculator B3 – allowed to automate production control operations. Several desktop variants of this calculator – MK – , MK – and MC (figure on the right) were manufactured. They were large desktop calculators with special sockets in the back. These sockets were linked to an additional register 9 used to store the “experiment name” code. In These calculators it was possible to input the data both from the keyboard, and from external systems such as gauges, analog-digital converters and other devices. They processed the data to carry out operations such as size tolerance in quality control, and to print the data and results with the help of external systems. The MK – 73 AKA MC differed from the MK – 57 by the availability of a built-in digital-to-analog converter. Many MK – 73 calculators were installed in physics laboratories of specialized technical schools, as they used to say, to measure the voltage of a battery.
[F] The most popular Soviet calculator. [F] [X] The first programmable calculators B3 – , MK – 55 and MK – 73, although worked under the control of a program, had only two operational registers X and Y, and working with the circular stack was very inconvenient. This was changed in (by the programmable calculator B3 – 46, with fluorescent display and priced at roubles. It was another step forward! It had a stack based on four registers, steps of program memory, 23 registers of memory instead of the seven available on the B3 – 32, and most importantly – the capability to organize cycles and work with index registers. It was a pleasure to work with this calculator. [X] (Soon, in , appeared its analogues, the B3 – and mk – 64, with fluorescent display and a more beautiful design, and costing on roubles cheaper at the expense of using a power supply of different type. The desktop variant MK – 65 was also developed. [X] One behind another, the most popular scientific and technical magazines, such as “Science and Life”, “Engineering – youth” and “Chemistry and Life,” started to teach how to work with the calculator. “Science and Life”, started in October a special section named “Man with the calculator”, talking about how to work with the B3 – 46, and including plenty of useful and game programs. The magazine “Engineering – Youth “, beginning in (included a column on programming the B3 – (under the name “The Calculator – your assistant” , and then organized the “Club of Electronic Games “, which printed the most fascinating and fantastic stories:” The True Truth “and” Way to the Earth “, here the readers were given the chance “to run into” the engineering of “landing” on a lunar surface and carry out a flight back from the Moon to the Earth by a ship, not adapted to such lunar flights, called the “Kon-Tiki”. School kids and adult calculator users waited with impatience the next number of “Engineering – Youth” to continue their flight back to the Earth … [X] This calculator worked under the Reverse Polish Notation system, therefore, after entering the first number, the
key is pressed, then the second number is entered and the corresponding operator key is pressed. For example, to multiply 2 by 3, it was necessary to press the keys: (result – 6). A stack consisting of four registers – X, Y, Z, T was used to store the operands. To enter a number after obtaining a result and to recall a number from one the memory registers (0 .. 9, A .. D), the content of the X register, which is the display register, had to be moved to the Y register, causing Y to move to Z, and Z to T. Registers X and Y were used for most operations requiring operands. [X] In programming mode the code for each command takes one cell of memory. Branching commands (transfers, loops, conditional transfers) take two cells. One cell for the operation code, and a second for the transfer address. In contrast with the B3 – , the transfer address can now be entered directly, instead of finding the correspondent operation code in a table. For example, to enter a transfer command to address (with the B3 – it was necessary to enter [BP] [3] (the 3 key corresponded to code 39, in the B3 – 41 calculator it was only necessary to enter [BP] [3] [3]. Although now one more keystroke is required, it is no longer necessary to look for the operation code in a table. [X] (More details on how to work with the B3 – calculator, are described on the special page devoted to the use of the B3 – located here [X^Y] ) [X] However, the most interesting aspect of the B3 – calculator and its analogues is the availability of (undocumented features) . These were useful not only to write programs, but also to build special display messages. There are so many undocumented features that they could deserve writing an additional article. [X] [*] (The B3 -) calculator and its analogues, the MK – 65 and the desktop MK – 65, became so popular, that the developers from the “Crystal” Kiev factory decided to continue this line. In (the new models MK – and MK – 61 were introduced. They had one more memory register, 5 programs of steps each, and ten additional functions. In addition, the MK – (calculator had) bytes of permanent memory, which was not erased when the power was disconnected. This memory was able to store both programs and data. The MK – 60 Calculator also had special sockets for the connection of available program modules known as BRP (blocks of memory expansion). When designing the BRP blocks the developers again killed two rabbits at once by soldering in one block the matrix for two sets of programs. By connecting a jumper, say, in rule 1, one had the block BRP-3 with a mathematical set of the programs, then re-soldering the jumper to rule 2 – the block became the BRP-2 with astro-navigational functions. Of course, this implied to lose the manufacturer warranty since to do that it was necessary to remove a sealed screw. This was divulged in one of the issues of “Science and Life” magazine by a reader who in turn was told by one of the “Crystal” developers. I can imagine what would happen to this developer. [F] [X] (By the way, the MK – flew to the space in the “Soyuz” TM-7 “, where it was supposed to compute the landing trajectory in case the onboard computer would fail. [F]
[F] (Late models of calculators) [BP] [X] Early calculat ors consumed a lot of energy from its batteries, providing a maximum of two hours of independent work. 302 volts were not always available, and replacement batteries where only available in large cities. Therefore, engineers and developers began to develop calculators with less power requirements. By that time, displays based on liquid crystals with low power consumption had already been invented. [F] [X] (The B3 – (shown at the left) became the second calculator based on liquid crystals after the B3 – 12. Developed in and consuming only 8 mW (for comparison, the B3 – (calculator consumed) (mW), this calculator had a function, unusual for Soviet calculators, to return the inverse of a number. This function is now available practically in all modern simple calculators. To calculate 1/5, the following sequence was used: [F] [-:-] [=]. In , the B3 – 40 calculator was replaced by the B3 – 51 model, in which the microchip used a new low-level logic. The power consumption was decreased by eight times to only one mW. This allowed to build this calculator without a voltage converter. [X] One year after, for the Moscow Olympiads of 1983, the MK – 60 Calculator was manufactured with an onboard watch, an alarm clock, and a stop watch. This calculator required one less battery than the B3 – . This became possible at the expense of using an even lower level microcircuit, the K VV3-2, which was considered to be “Bodiless”. [=] [X] A new milestone in the development of calculators was the MK – 69 which was powered by a solar cell. In general, this was a simple calculator with one memory register, nothing special except for the solar batteries. [X] The creativity of the engineers did not rest, and deciding that miniaturization was important, they developed in a new super- small, but very clever calculator, the B3 – 51. It included all the last achievements of micro-electronics. Its dimensions were the smallest available at the time – (x) x 5.5 mm. It was able to perform not only scientific, but also statistical calculations. This calculator had two prefix keys – F1 and F2. [X] (A similar calculator was introduced in 2019, but with larger size, the MK – . Soon it became very popular, although it had a basic defect – the worst power switch ever made. Engineers had decided to include a mechanism consisting of a semicircular toddler, which closed the contacts on a wiring attached directly to the printed circuit board. Certainly, with the pass of time the contact points got rusted and became defective. [F] [X] These calculators used for the first time the “digit by digit “(CORDIC) method for the calculation of transcendental functions which has replaced the Taylor finite-series approximations of a number. CORDIC was the standard in Almost all modern calculators all over the world, except at the USSR. In two words, the “digit by digit” method allows to calculate an attribute by iteration and tabulation. It is characterized by the simplicity in the execution of operations (algebraic addition and shift), the significant similarity of the algorithms applied for various functions and, most importantly, for the high speed and accuracy of the calculations. The margin of error in calculations for an 8-digit argument was at most / – 1 in the seventh or eighth digit. [X] Finally, one of the latest models among engineering calculators was the MK – 90 standard calculator powered by solar components. As a matter of fact, it was a continuation of the series B3 – and MK – 57. As opposed to the B3 – 51 and MK – models, this calculator, as well as the C3 – , used an algebraic logic with five levels of brackets for calculations. It also worked with simple fractions, and could display the results in degrees, minutes and seconds. It had hyperbolic functions, and a mechanism to round-off the result to a required accuracy. In addition, it was a ten-digit calculator. [X] There is one more direction in the development of calculators – the demonstration calculators. As a matter of fact, these were normal calculators wired to large displays and magnetic buttons. A hand magnetic pointer was used to activate the keys. I only have one photo of the demonstration calculator made on the basis of the MK – 51. On one occasion I attended a demonstration in my school with a calculator compatible with the MK – 61 measuring 1.5 meters, but by the end of August it had been thrown out on the rubbish dump … [F]
[sin] (Calculators bugs and features **) [X] This section is a brief review on errors and special features of Soviet calculators. Taking into account the special circumstances of the development of Soviet calculators, including the geopolitical aspects, it becomes clear that if Soviet engineers developed the calculators not basing the design on a level-by-level scanning of the microcircuits of their imported analogues, they were constantly introducing some highlights into their work. There were either errors in the calculations performed by the calculators or interesting discoveries. [X] As an example, the family of calculators belonging to series B3 – (B3 – [F] , B3 – (G, MK -) ), indicated the availability of a number in the memory register by displaying a dot in the leftmost display position. On the other hand, this calculator perfectly calculated square roots for negative numbers. The square root of -4 was reported as -2, and no error messages were displayed. ** [X] (In the B3 – calculator, when the Developers realized that There was a dot at the left of the display which was not involved in any operation, they decided to involve it. In this model this dot lights up while a key is pressed and turns off when it is released. Any more problems to solve?. [X] (In the calculators of the B3 – (family B3- , MK – , MK – 55) although the developers implement the calculation of a factorial by an ordering method (1 2 3 …), they forgot to block the keyboard when an error message was displayed, so the user was able to continue the operations with the erroneous results. [X] (In the B3 – calculator, the developers included a function which stored the sine of the argument in the Y register, and the cosine in the X register. Then, by simple division, the user could obtain the tangent. Very convenient. However, an error was detected on the first series of These calculators: when adding a number containing seven nines in the mantissa and a nine in the eighth digit, which is not displayed – to a number larger than four, an error occurs. for example, adding 9. to (yields) . [X] When executing complex operations like getting the sine of of a number, one of the registers in the circular stack could be trashed. To check if a calculator has this problem, enter [2] [CN] [BP] [F]. If the display shows 1. – 09, Then the calculator has the bug. [*] [X] In addition, some models perform incorrect jumps to the subroutine if a PP operator is entered into a cell of program memory with address 69, , 85, 91, or , and an operator with a code equal to the subroutine transfer index is executed. This is a little difficult to understand, but if address 61 contains the symbols | PP | 9 | 9 | S / P |, instead of jumping to address 112 (code for key | 9 | – 112), the calculator fills the register X with the number . This could easily cause bewilderment and a nervous breakdown to the programmer, who was sure that the program has been written correctly. [F] [X] Curious users can find in the MK – 91 calculator a very remarkable feature. The switch for “grades-radians-degrees” falls easily into an intermediate position – between degrees and radians, or between radians and grades. Who had hit upon this idea before? At this point, the calculator turns into a very unusual mode of calculations reminding the operation of the MK – 57 calculator. First, now the numbers in the microprocessor have a mantissa of length 8 instead of ten, the missing digits are still kept in memory but are no longer visible to the user. Secondly, some function keys have a different functionality! The key showing degrees now calculate the 1 / x function when used with the factorial function “F”. The 1 / x key – switches the method of calculation of trigonometric functions (degrees – radians – grades). The display, however, still shows the corresponding “F”, “P”, “K” icons! If the “F” key is combined with the 1 / x key the calculator mode passes to statistical calculations. The “hyp” key now process the information in degrees, minutes and seconds, and goes back to its normal mode if the “F” key is pressed. Segments of the leftmost positions in the display are used to indicate that a number is stored into the “P” memory, or the inverse (shift, 2nd) mode “F” is active, or a constant “K” is being applied to the calculations. [*] [X] And now, the B3 – , the most common calculator in Russia. This calculator has plenty of errors and operational features. Only some of them will be described, the ones that once were mentioned in a book as being features “… are a consequence not of errors made by the developers of the microprocessor, but of their attempts to find a compromise between the software requests and simplicity of the design. “When executing operations under a programmed mode, the functional operators preceding the / – / operator default to a sign change. After some operators transfer the control to the end of a subroutine, instead of returning the control to the V / O operator, the next operator is executed. Here such “feature”. The operator X ^ Y was executed incorrectly in order to keep significant figures in the operands. For example it is possible to enter [5] [5] [5] [3] [X] [F] . If [max] is displayed, the operator X ^ Y is calculated incorrectly. These errors were corrected subsequently, but there were errors on building negative integer numbers, the MK – and MK – calculators chose zero as the largest value when the function to evaluate the maximum of two numbers [X^Y] [max] were used. Take my word, “we have” tried. [*]
[F] (Epilogue) [X] Well here we are, and I hope I have not tired you. Please send your comments and wishes directly to my address: [email protected] . [X] I also collect microcalculators. I have more than 57 unique models of Soviet calculators, more than books, about [sin] magazines and other calculator related items. Visit my web site, devoted to collecting microcalculators: (http://www.geocities.com/SiliconValley/) / calcolle.htm [*] [X] My collection is for sale! If you became interested in Soviet calculators, visit the site of my friend Andrew Davie from Australia located at (http://www.comcen.com.au/~adavie/slide/calculator/soviet.html . On this museum you will find not only a complete list of Soviet calculators with images, but also a reference to other interesting sites related with calculators. [X] Good luck! [X] (Sergei Frolov) (Read More) [*]

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