Jaap's Mechanical Calculators Page

The Pocket Adding Machine

The Pocket Adding Machine

My Pocket Adding Machine
How To Use a Slide Adder

The slide adder was invented by Claude Perrault in France some time in the second half of the 17th century. His machine was called the "Abaque Rhabdologique". It was however Heinrich Kummer who in the 1840s created the first version where the carry from one digit to the next was performed by moving the stylus around a hook-shaped slot.
The slide adder increased in popularity in the 1920s, when Carl Kübler produced a very cheap version called the Addiator. Soon dozens of different versions appeared on the market, and they offered a relatively cheap aid to calculating sums. They had names such as Addiator, The Pocket Adding Machine (see below for the one I own), Ve-Po-Ad (Vest Pocket Adder), Produx, Pro Calculo, Correntator, Picma, Arithma, Toto, Addmaster, and many, many more. They found a revival in popularity in the 1950s and 1960s, and versions of such machines continued to be produced until the 1970s, after which cheap electronic calculators became the norm.

Slide adders are usually made of thin metal sheet, and come with a metal stylus. On the front there are several vertical slots, with a toothed slider inside. Beside each slot there are the digits from 9 (top) to 0 (bottom). Above the slots is a register, consisting of a hole above each slot through which a digit is visible.

My Pocket Adding Machine

The Pocket Adding Machine sits in a fake alligator-skin case, made of cardboard. It is designed for sterling currency, with 5 digits for the amount of pounds. Note that the slider at the far left is not directly accessible, and only registers the overflows from the adjacent slider. This means that you can only add amounts of up to 4 digits (i.e. up to £9,999), though the eventual total may have 5 digits.

The outer case has some red discolouration, and a small spot of damage on the back. The machine itself is in good working condition, though with some minor stains on the metal.

It is not certain who manufactured the Pocket Adding Machine, though it is believed to be Otto Meuter after he left the Addiator Company. It was produced in the early to mid 1920s. It has no serial number. The Pro Calculo was an almost identical machine, obviously from the same maker, except that it had only decimal sliders and a different name embossed at the top.

The Pocket Adding Machine, case front
The Pocket Adding Machine, case back
The Pocket Adding Machine, partly removed from case
The Pocket Adding Machine, front
The Pocket Adding Machine, stylus in case
The Pocket Adding Machine, stylus removed
The Pocket Adding Machine, logo
The Pocket Adding Machine, sliders on zero
The Pocket Adding Machine, sliders on maximum
The Pocket Adding Machine, clearing tab
The Pocket Adding Machine, clearing tab fully extended

This is the instruction leaflet that comes with the machine.

The Pocket Adding Machine, Instruction leaflet, front
The Pocket Adding Machine, Instruction leaflet, addition
The Pocket Adding Machine, Instruction leaflet, subtraction
The Pocket Adding Machine, Instruction leaflet, back

The Pocket Adding Machine, Instruction leaflet, front
The Pocket Adding Machine, Instruction leaflet, addition
The Pocket Adding Machine, Instruction leaflet, subtraction


How To Use a Slide Adder

To add a number, you place the stylus in a gap between the teeth of a slider next to a particular number, and slide the stylus all the way down. This shifts the slider the chosen number of steps, so that the number shown in that column of the register is increased by that amount.
The sliders generally only slide down at most 9 steps. If adding your chosen digit were to push it above 9, then a different action is needed. You can recognise this either by the fact that your stylus doesn't go all the way down, or by the fact that the teeth next to the stylus have a red dot painted on them. If that is the case, then instead of sliding it down, slide it all the way up, then move the stylus to the left and then down a bit. These last movements let the stylus engage with the next column and pull it down one step, thus adding a carry to that next column.
If this method of automatically carrying to the next column is blocked, then that next column is already showing a 9. In this case you will have to add a 1 to that next column in the normal manner, i.e. put the stylus next to the 1 in that column, and bring it all the way to the top, and then left and down to carry to the column after that. If that is blocked too, you have to repeat that action again for the next column, and so on.

Subtraction is essentially the reverse of addition, and can be done by reversing all the actions of addition. Some slide adders however have below the slots used for addition a second set of slots which are used for subtraction. These have 'hooks' at the bottom instead of the top so that you can move your stylus to the bottom and then left and up, to borrow from the next column up. Some slide adders have the subtraction slots on the reverse side of the machine instead of above or below the addition slots.

To clear the register, pull the little tab at the top of the machine. This pulls all the sliders upwards with it, until every digit in the register is zero. Then push the tab back down before starting the next calculation.

Some slide adders (such as The Pocket Adding Machine) are actually designed for adding Sterling currency. The rightmost column is for farthings, and shows only 0, 1/4, 1/2, or 3/4. The column to the left of that is for pence, and goes from 0 to 11. The next two columns are for shillings, so there is one normal 0-9 column and one short column that only has the number 0 and 1; these two columns together give you 0 to 19. This is followed by a number of normal 0-9 sliders for an amount of pounds.
Note that the short shillings column usually does actually have a full length slider, so that the number of shillings displayed can go up to 99. If it goes above 19 you can convert those shillings to a pound by adding 0 to that short column, i.e. putting the stylus in the 0 gap, and bringing it to the top, then left and down to increase the number of pounds. You can repeat this as often as necessary to bring the number of shillings to below 20.

Advertisements and Articles

Here are a couple of advertisements from online archives.

1922-03-20 Sheffield Daily Telegraph
1922-05-17 Belfast News-Letter
1922-05-26 Birmingham Daily Gazette
1926-07-17 The Queenslander (Brisbane)


PatentFiling datePublish dateNameDescription
US 90,27518-05-186918-05-1869Henry KummerSlide adder with hooked slots.
DE 356,78213-04-192028-07-1922Carl KüblerFront plate with hook-shaped slots.
DE 367,59924-05-191923-01-1923Carl KüblerAdder with subtraction slots on reverse. See also AT 94,048B, CH 98,349, FR 524,987, GB 148,455, US 1,596,108.
DE 368,82906-02-192110-02-1923Carl KüblerSmall strut for holding the guide rails of the sliders.
DE 398,77213-04-192015-07-1924Carl KüblerExtra long sliders with numbers 10 and higher, for easier calculations.
DE 405,33402-10-192103-11-1924Carl KüblerRibbed or sunken teeth to avoid red markings being rubbed off.
DE 408,03223-07-192208-01-1925Carl KüblerSliders adapted for weights, times, or Sterling currency. See also GB 201,168.
DE 411,75102-10-192101-04-1925Carl KüblerAlignment mechanism for sliders
DE 415,18920-11-192315-06-1925Jean BergmannFront plate that flips over for subtraction, used in the Correntator.
DE 416,10522-01-192406-07-1925Jean BergmannFlippable front plate with separate register for subtraction. See also US 1,661,277
DE 416,56423-03-192020-07-1925Carl KüblerExtra long sliders with blanks above 9 and below 0, for easier carry/borrow actions. See also CH 102,321, GB 172,909.
DE 423,73012-04-192508-01-1926Jean BergmannSpecial stylus
DE 423,73126-03-192509-01-1926Jean BergmannSubtraction slots above addition slots
DE 586,918(?)22-08-193012-10-1933Carl KüblerSliders with blanks above 9 and below 0, for easier carry/borrow actions See also CH 163,596, GB 387,728, US 1,961,053.
DE 1,387,966U24-03-193622-10-1936Carl KüblerSlide adder that also displays negative numbers. See also AT 131,301B.


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