Electromechanical calculating machines from the 1960's
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Other calculating devices

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A mechanism that is capable of adding multi-digit numbers. This consists of a register with a carry mechanism, a feed mechanism to enter the successive values into the register, and usually some means of restoring the digits to zero at the end of a calculation. Unlike a counter register, which is fed only through its lowest order digit, many digits of an accumulator can be fed simultaneously. This requires more careful sequencing of the carry mechanism to avoid jamming. The results register is an example of an accumulator, but a revolutions register is typically only a counter.

adding machine
This term is commonly applied to any calculator that prints results on paper tape, however, in the context of this site it is specifically a two-function machine capable of addition and subtraction, but not multiplication or division. This scope of this collection does not include adding machines.

adjustable pawl
Also referred to as “selectable ratchet” or “Hamann mechanism” because there is no good English translation for the German word “Schaltklinke”. A feed mechanism that consists of a cylindrical cam surface that is adjustable, with a variable portion of the surface at a reduced radius. A pawl acts as a cam follower, engaging and turning an annular gear when it falls into the portion of the cylindrical cam with the smaller radius. Generally attributed to Christel Hamann, this feed mechanism was used exclusively on the Hamann machines. See this diagram.

automatic multiplication
Upon separate entry of the multiplier and multiplicand, a machine with automatic multiplication will compute the product at the push of a single button. This requires the machine to have an additional register to allow it to store one factor of the equation, (the control register) with the other factor stored in the input register.

back transfer
For problems involving chain multiplications (multiplications with more than two factors, e.g. 60 x 24 x 365), the machine needs to be able to use the product of the first two factors as an input for the remaining multiplications. Mechanically, this involves being able to move the value in the results register into the control register.

The capacity of a register refers to how many digits it has. The capacity of a machine is the combined capacity of its registers. It is written as a x b x c, or the capacity of the input register x revolutions register x results register.

carry mechanism
In the event of an overflow in a digit of a register, the carry mechanism increments the adjacent digit by one (for addition) or decrements by one (for subtraction). For example, the equation 9 + 1 = 10 requires a positive carry from the ones-digit to the tens-digit.

The tens complement of a number is that number subtracted from the next highest power of ten. For example, the tens complement of 123 is 877. In most rotary calculators, negative values are shown as their tens complement up to the capacity of the register. For an eight-digit register, the value -123 would be displayed as 99999877. A machine with credit balance can display negative numbers as their true value.

control register
Also referred to as the "multiplier register". In machines with fully automatic multiplication, this register stores the value of one of the factors so the machine knows how many times to successively add the value in the input register. Some machines do not have this register, instead calculating the product for each digit of the multiplier individually as the digits are being entered. This method is called semi-automatic multiplication.

counter register
A register incorporating a carry mechanism, such that successive inputs into the lowest order digit will yield the correct count up to the capacity of the register. This type of register can only accept inputs into one digit at a time, unlike an accumulator which can accept inputs into multiple digits simultaneously. The revolutions register is an example of a counter.

credit balance
A machine with this feature can display negative numbers as their true value instead of their complement. Almost no rotary calculators have this feature, but it is rare to find a printing calculator without it.

cycle speed
The speed of the main drive shaft of the machine, which is directly proportional to the speed of calculation.

duplex machine
A machine with two completely separate results registers.

feed mechanism
This mechanism is the heart of the calculating machine. It transfers the value from the input register into an accumulator. Each digit of the feed mechanism can be set to a value from zero to nine, which is then transferred to the accumulator in a single machine cycle. Examples of feed mechanisms can be seen on the Mechanisms page.

four-function machine
A machine capable of addition, subtraction, multiplication and division.

full keyboard
This is the large rectangular array of keys commonly found on rotary calculators. It consists of a column of 1-to-9 keys for each digit of the input register. There are usually no keys for zeroes, which are “entered” by not pressing any key in that column.

fully automatic calculator
Once the factors of a problem are entered into the machine, a fully automatic calculator can compute the answer at the press of a single key or lever. This requires a motor to drive the machine, a means of storing the factors in the machine, a function key for each operation that can trigger the motor to begin the calculation, and mechanisms to determine when the calculation is complete. All the machines in this collection (with a couple exceptions) are fully automatic calculators.

input register
This register stores values as they are entered into the machine by the operator. For a calculator with a full keyboard, the keys lock into place when pressed, thereby serving as the input register. In some machines, this is accompanied by a visible register to confirm the value entered. In machines with a ten-key keyboard, there is usually a pin carriage that records the subsequent digits entered on the keyboard.

machine cycle
A machine cycle is usually a single revolution of the main driveshaft. Each revolution is divided into a portion that drives the feed mechanism, followed by a portion that drives the carry mechanism.

memory register
This is a separate register that allows a value to be stored from another register in the machine, and then recalled to the keyboard. Which register can be stored in the memory varies from machine to machine.

oscillating rack
Also referred to as “rocking segment”, this is a feed mechanism more commonly found on adding machines. A toothed rack moves back-and-forth, engaging a counter register in one direction only. Since half of the motion is not used for calculation, this mechanism is slower than ones using a rotary principle. See this diagram.

pendulum wheel
A feed mechanism unique to the Olympia calculators consisting of an internal register that moves between a series of oscillating racks and an accumulator. Once the racks set a value in the internal register, it can be used to input the value into the accumulator as many times as required.

Also referred to as an “Odhner wheel”. This feed mechanism is a gear with a series of teeth that can be retracted radially, allowing the number of active teeth can be set anywhere from 0 to 9. See this diagram.

pin carriage
On a machine with a ten-key keyboard, there is a sliding assembly with a matrix of bistable pins to serve as the input register. As each digit is entered on the keyboard, the corresponding pin for the number entered is depressed, and then the carriage is shifted by one digit.

printing calculator
This is a fully automatic calculator with the ability to print the results on a paper tape. Unlike an adding machine, a printing calculator can automatically multiply and divide. Although electronic calculators of the 1960’s could easily display results using Nixie tubes or CRT’s, printing was still a mechanical process. As a result, electromechanical printing calculators survived in the marketplace longer than rotary calculators, well into the mid-1970’s.

proportional gear
A feed mechanism unique to Marchant calculators, invented by Harold Avery. Each digit of the machine has a nine-speed transmission. This, combined with very high cycle speeds of 1300 rpm, made the Marchant the fastest electromechanical calculator ever produced. See this diagram.

proportional lever
Another feed mechanism designed by Christel Hamann. This mechanism was used exclusively on Mercedes-Euklid (later known as Cellatron) machines. A lever attached to nine separate racks moves in an arc, pulling each rack an incrementally greater distance. Pinion gears for each digit can slide to engage any one of the nine racks. See this diagram.

This is simply a mechanical representation of a number. It can be visible, like the rows of number wheels on a carriage that show the result of a calculation, or hidden, as in the control registers or memory registers of some machines.

results register
This is the largest register in the machine, and displays the accumulated value of successive additions or subtractions. For addition, subtraction or multiplication problems, the answer is read on this register. For division problems, this register is used by the machine to determine when to shift the carriage over to the next digit: the machine subtracts the divisor from the dividend repeatedly until this register goes negative (overdraft), then the carriage is shifted one place and the divisor is added once to restore value to a positive number. This continues for each digit in the quotient.

revolutions register
This register counts the number of times the machine cycles. At the end of a multiplication problem, the value of the multiplier can be confirmed here. For division problems, the answer (quotient) is read on this register.

ripple carry
This occurs when the carry from one digit causes a carry in the next, for example 999 + 1 = 1000.

rotary calculator
These machines have feed mechanisms that use rotary motion, keeping the mechanism engaged and in motion at all times. Linear mechanisms, such as the oscillating rack, move in one direction, then must stop and disengage before restoring to its original position for the next machine cycle. The more efficient use of machine cycles in a rotary calculator means they are usually faster for multiplication and division problems. On this site, the term “rotary calculator” is extended (unfairly) to include any machine that does not print, and excludes the few printing calculators that use rotary feed mechanisms for some of their functions.

semi-automatic multiplication
A method of multiplication that calculates the product for each digit of the multiplier individually as the digits are being entered, then automatically shifts the carriage to the next higher place before the next digit of the multiplier is entered. This avoids the need for a control register, but often requires the digits of the multiplier to be entered in reverse order. If the machine is not very fast, the operator must wait for the machine to finish one digit of the multiplier before entering the next.

shortcut multiplication
This is a method of multiplication that reduces the required number of machine cycles, effectively increasing the speed of the calculation. For example, when multiplying a value by 8, the machine subtracts the value twice, shifts the carriage over one digit, and then adds once. In equation form, this would be: 8n = 10n – 2n. This example requires only three machine cycles compared to eight in a machine without this feature.

stepped drum
Also referred to as “Leibnitz wheel” after its inventor, Gottfried Wilhelm Leibnitz (1646-1716). This feed mechanism is comprised of a cylinder with nine gear teeth, each tooth incrementally longer than the next. A thin pinion gear can slide axially to engage a different number of teeth depending on the position of the gear along the length of the stepped drum. See this diagram.

ten-key keyboard
This is the familiar keyboard layout of modern electronic calculators, with the digits 0 to 9 arrayed in four rows. Some mechanical calculators, such as the Facit CA1-13, used a variation on the theme, with two rows.