Jaap's Mechanical Calculators Page


Walther RMKZ

My Walther RMKZ

This calculating machine is a Walther RMKZ. It was made by Walther, a German company better known for making weapons such as the Walther PPK that James Bond is so fond of. Walther started producing calculators around 1924, and apparently produced this model between 1931 and 1952.

It uses a pinwheel mechanism, sometimes known as an Odhner mechanism. This means that when you enter a number by moving a tab up or down, pins are extended or retracted on an internal wheel, until wheel has the same number of extended pins as the digit you selected. When the handle is then cranked, the pinwheel turns and engages with another cog wheel which then rotates the chosen number of steps. The pinwheel seems to have been patented first by David Isaac Wetheimber in 1843 (GB184309616) but it was Willgodt Odhner who came up with the standard design of the pinwheel calculator.

The main body of the machine contains has 10 tabbed wheels, with the tabs extending through vertical slots in the casing. By moving these tabs you select a number. This selected number is displayed in the register at the top of the machine.

The front of the machine has a carriage that can move left or right. This carriage shows two registers. The left register is an 8-digit revolution counter, and the right register is a 13-digit accumulator.

On the right hand side is a crank with which the selected number is added to (or subtracted from) the accumulator. There are also two levers which shift the carriage one position to the left or right. The carriage also has two small crank handles, one on each side, that are used to clear the registers. The button on the front of the carriage releases it so that it can be shifted quickly any amount left or right.


Normally you start with the carriage shifted all the way to the left. When you crank the handle clockwise once, the input number on the pinwheels will be added to the accumulator on the right of the carriage. The revolution counter on the left of the carriage is incremented.
You can shift the carriage one column to the right, and if you then crank the handle again, ten times the input number is added to the result, and ten is added to the revolution counter. In this way you can add any multiple of the input to the results, and the multiple that you have added is shown in the revolution counter.

I think the rest of this description only applies to 'Z' models (e.g. RMZ, RKZ, RMKZ) which have a carry mechanism in the revolution counter.

You can turn the crank handle in opposite direction, anti-clockwise, to subtract the input number from the accumulator. Note that this also decreases the revolution counter. This allows you to multiply a number by for example 9 with only two cranks of the handle instead of 9, by adding it once in the tens column and subtracting it once in the units column. Afterwards the revolution counter will display 9, the multiplier that was used. In other words, the revolution counter keeps track of how many times the input number has been added to the accumulator, regardless of how that was achieved.

There is a switch lever on the top-left of the main body. Flipping this switch changes the direction in which the revolution counter is changed. Instead of counting how often the input has been added to the accumulator, it then counts how many times the input has been subtracted. This allows you to do division as follows. Put the number you want to divide in the accumulator register. Most models allow you to do this manually, turning the accumulator digits with your fingers, but you can also do it indirectly if necessary (clear accumulator, input the number add it to accumulator once, clear the revolution counter). Input the denominator. Now flip the switch to reverse. Now subtract multiples of the input to get the accumulator as close to zero as possible. The revolution counter shows how often it was subtracted, i.e. it gives the quotient. Whatever is left in the accumulator is the remainder of the division.


The data for the table below is taken from the two sites Rechnerlexikon and Rechenmaschinen Illustrated. Unfortunately, their information sometimes contradicts each other, and then I have chosen whichever data seems more plausible.

Walther made many models of pinwheel calculators, and this list is probably not even complete. The letters in the model name have the following meanings:
M - has a larger input register (10 instead of 6 digits).
K - has a display showing the input number
Z - has a carry mechanism in the revolution counter and a subtraction switch.
D - has automatic division
E - electrically powered
W - back transfer mechanism (copies accumulator into input).

ModelYearsKnown S/N rangeDigitsSizeWeightColourRemarks
Walther 1 1925-19??1,482-2,8929x8x1329x13x10cm4.5kg
Walther 2
Walther 3
Walther DMKZ 1933-193812,155-14,27010x8x13
Walther DRKZ 1933-193617,272-17,2746x6x10
Walther EM 1927-1928?7,90710x8x1334x20x14.5cm8.5kgRevolution counter does have carry mechanism
Walther EMKD 1929-19459,497-30,48110x8x13 & 10x8x1620x30x14cm10kgblackRevolution counter does have carry mechanism
Walther R 1929-1938?18,9256x6x10black
Walther RK 1929-1938?4,484-16,4636x6x10black
Walther RKZ 1933-1938?17,428-27,1696x6x1030x13x13cm4kgblack
Walther RKZ-10 1949-195253,788-108,2466x6x1032-4x13x14cm4kgblack
Walther RM 1933?-1938?3,598-7,961 & 21,010-22,46210x8x13 & 10x8x1613x25x124.4kgblack
Walther RMK 1929?-1938?3,911-16,09910x8x13 & 10x8x1630x12x13cm4.9kgblack
Walther RMKZ 1931-1945 &
25746-39891 &
10x8x13 & 10x8x1626x22x14cm3.8kgblack
Walther RMZ 1933-1938?11,814-16,09210x8x13 & 10x8x16black
Walther SMKZ 1933-193621,053-21,05810x8x1331x15x13cm6kgblackSecond storage accumulator on carriage.
Walther WR 10 1950-195470,170-71,3986x6x10green
Walther WR 16 1950-195460,356-63,60210x8x1636x13.5x13cm4.3kgblack, green
Walther WSR 11 1953-1956120,123-121,4196x6x114kggrey
Walther WSR 16 1952-1957102,253-113,974 & 222,71310x8x1628x15x13.5cm5kggrey, green
Walther WSR 1101956-1968?115,633-116,1736x6x1115.6x29.0x13.9cm4.65kggrey, beige, green
Walther WSR 1601956-1968?102,253-214,90810x8x1615.6x29.0x13.9cm4.65kggrey, beige

My Walther RMKZ

This RMKZ is in fairly good working condition. It does however have some damage, namely the part of the body holding the crank handle has cracked and one of the input display digit wheels is damaged slightly. The latter is purely cosmetic damage, the former does not interfere with the working of the machine.

At some point, possibly in the 1950s, it has been refurbished, and its original black paint was changed to a metallic hammer grey enamel. This enamel is chipped at the left edge of the carriage, but otherwise looks very good.

Its serial number is 10,890. This unfortunately conflicts with the information from some other sites which state that the numbering for this model started at 20,001. If that is mistaken, then this is an early model which was probably made somewhere between 1931 and 1935. However, even if those other sites are correct and the serial number 10,890 was incorrectly applied to this machine, then I would still deem it likely that this is a pre-war RMKZ because of it having been refurbished after the war.

The rear panel has stamped in it the writing "CARL WALTHER, Abt. Rechenmaschinen, ZELLA-MEHLIS Thün".

Walther RMKZ
Walther RMKZ, top view
Walther RMKZ, right view
Walther RMKZ, left view
Walther RMKZ, rear view
Walther RMKZ, serial number
Walther RMKZ, text
Walther RMKZ, inside view
Walther RMKZ, broken crank rest


In this video I demonstrate how to do addition, subtraction, multiplication, and division.


PatentFiling datePriority dateNameDescription
US 209,41613-07-187829-10-1878Odhner, W.Pinwheel calculator
DE 545,53310-12-192902-03-1932Walther, CarlSubtraction switch
DE 621,31613-10-193405-11-1935Walther, CarlBack transfer mechanism


Wikipedia entry for the Carl Walther, the founder of the Walther company.
Rechnerlexikon has pictures and details of many models
Rechenmaschinen Illustrated has pictures and details of many models
John Wolff's Web Museum's Walther page

© Copyright 2015 Jaap Scherphuis, .