Jaap's Mechanical Calculators Page


Walther RMKZ Walther WSR 160

Walther RMKZ
Walther WSR-160
Books and Manuals

Walther RMKZ

The Walther RMKZ is a calculator based on the classic Odhner pinwheel calculator design. My machine 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. I have not found any other example of an RMKZ with such a low number. It must have been one of the earliest, probably from 1931 when this model was first made. By 1936 the numbering was up to 20,000.

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.

Walther WSR-160

The Walther WSR-160 is the last model pinwheel calculator that Walther made. It was in production from about 1956 until 1968 or possibly 1971. It was also sold using other brand names, for example in Great Britain it was called the Muldivo Mentor. My machine is in working condition, although one of the input pins is hard to move.

Compared to the RMKZ there are several improvements in its design:

Walther WSR 160
Walther WSR 160
Walther WSR 160
Walther WSR 160
Walther WSR 160
Walther WSR 160
Walther WSR 160
Walther WSR 160
Walther WSR 160

Its serial number is 194,935 which means it was probably made in around 1967. The label in the back says Walther Büromaschinen G.m.b.H., Niederstotzingen/Wttbg., with the model and serial number. The serial number can also be found on the carriage.

Walther WSR 160
Walther WSR 160
Walther WSR 160
Walther WSR 160
Walther WSR 160
Walther WSR 160


In this video I demonstrate how it works, including two methods of division.


Carl Walther GmbH is a German company better known for making weapons such as the Walther PPK that James Bond is so fond of. Carl Walther founded his company in 1886, making hunting rifles and selling them in his gunshop in Zella-Mehlis. From 1908 the company started making pistols instead of rifles. Carl died in 1915, and from then on the company was run by one of his sons, Fritz Walther.

The treaty of Versailles at the end of World War I severely restricted arms manufacturing and trade, so Walther had to diversify. In 1924 they started producing calculators. This came about in cooperation with Mercedes, who had a factory in Suhl just a few kilometres away from Zella Mehlis. Mercedes made pinwheel calculators under the Melitta brand, but wanted to focus their production on the Mercedes-Euklid type of machine. Walther then took over the production of the Melitta calculators, and were allowed to sell them under the Walther brand name, too. Soon they started developing them further, including electrically driven models. In 1931 they also manufactured the Tasma, an adding-listing machine with a full keyboard which had until then been made by Thales, though it seems this was never sold under the Walther brand name.

The Walther factory was destroyed in the second world war, no doubt due to its arms manufacturing activities. Zella-Mehlis was in the Soviet-occupied region of Germany, and Fritz Walther decided it was better to rebuild the company and factory in the Allied-occupied region. He and some of his engineers settled in Heidenhelm, where they set up a basic workshop. In about 1947 they were ready to set up a factory to manufacture calculators in the nearby town of Gerstetten and then another in Niederstotzingen. A few years later in 1953 the company had grown enough to restart the arms manufacturing in a new factory Ulm, at which point the calculator business was split off as a separate company, Walther Büromaschinen GmbH.

From 1952 they also started making electrically driven, 10-key adding-listing machines, such as the Walther SR-12. This machine was also sold in the USA by Felt & Tarrant under the name Comptograph 202. Fritz Walther died in December 1966, and was succeeded by his son Karl-Heinz Walther. By the late 1960s the WSR-160 was the only remaining pinwheel model still in production, but its end date is somewhat uncertain (some sources say 1968, others 1971). The other desk calculators became more electronic, and remained in production until the mid 1970s. The Walther Büromaschinen company went public and then became Walther Electronic AG, and later specialised in scanning and sorting machines under the name Walther Data GmbH.


The data for the table below is mostly 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 possably not 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 rangeDigitsRemarks
Walther 1 1926-19271,482-2,8929x8x13
Walther 2
Walther 3
Walther EM 1927-1928?7,90710x8x13Revolution counter does have carry mechanism
Walther EMKD 1929-19459,497-30,48110x8x13/16Revolution counter does have carry mechanism
Walther R 1929-1938?18,9256x6x10
Walther RK 1929-1938?4,484-16,4636x6x10
Walther RM 1929?-1938?3,598-7,961 & 21,010-22,46210x8x13/16
Walther RMK 1929?-1938?3,911-16,09910x8x13/16
Walther RMKZ 1931-194510,890-39,89110x8x13/16
Walther RMZ 1933-1938?11,814-16,09210x8x13/16
Walther RKZ 1933-1938?17,428-27,1696x6x10
Walther DMKZ 1933-193812,155-14,27010x8x13
Walther DRKZ 1933-193617,272-17,2746x6x10
Walther SMKZ 1933-193621,053-21,05810x8x13Second storage accumulator on carriage.
Walther RMKZ 1948-195751,798-81,50510x8x13/16
Walther RKZ-10 1949-195253,788-108,2466x6x10
Walther WR 10 1952-195470,170-71,3986x6x10
Walther WR 16 1952-195460,356-63,60210x8x16
Walther WSR 11 1955-1957120,123-121,4196x6x11
Walther WSR 16 1955-1957102,253-113,97410x8x16
Walther WSR 1101956-1968?115,633-116,1736x6x11
Walther WSR 1601956-1968?102,253-222,71310x8x16

Books and Manuals

Montage-Anleitung für Walther Rechenmaschinen Mod. WSR 110/160    (PDF, 8.85 MB or archive.org)
Metallwarenfabrik J. A. Heinrich Dankers
18 page booklet
148mm × 205mm × 1mm

This booklet shows how to fully disassemble the Walther WSR 110/160, so that all the parts can be thoroughly cleaned.

Montage-Anleitung fuer Walther Rechenmaschinen Mod. WSR 110/160
Montage-Anleitung fuer Walther Rechenmaschinen Mod. WSR 110/160
Montage-Anleitung fuer Walther Rechenmaschinen Mod. WSR 110/160
Montage-Anleitung fuer Walther Rechenmaschinen Mod. WSR 110/160


Here are some advertisements I found in online archives.

1925 Jarlibro de Universala Esperanto-Asocio
1930-03-19 Het Vaderland
1930-03-23 Het Vaderland
1930-04-02 Het Vaderland
1939-20-12 Algemeen handelsblad voor Nederlandsch-Indie
1940-03-18 De locomotief


Here are just a few of the relevant patents.

PatentFiling datePriority dateNameDescription
US 209,41613-07-187829-10-1878Willgodt OdhnerPinwheel calculator
DE 480,80505-11-192618-07-1929Carl Walther WaffenfabrikElectric drive
DE 545,53310-12-192902-03-1932Carl Walther WaffenfabrikSubtraction switch
DE 621,31613-10-193405-11-1935Carl Walther WaffenfabrikBack transfer mechanism
DE 845,11026-09-195005-06-1952Otto BarthelmesImproved carry switch
DE 925,43205-11-195024-02-1955Otto BarthelmesStationary input pins
DE 927,83525-11-195221-04-1955Walther Büromaschinen-GesellschaftCarriage return on clear
DE 971,53613-12-195129-01-1959Walther Büromaschinen-GesellschaftRegister clearance selection
DE 1,601,200 U23-09-194819-01-1950Fritz WaltherComma indicator design
DE 1,601,201 U23-09-194819-01-1950Fritz WaltherNumber wheel design


Walther, the company's website contains a page with history of the company.
Wikipedia entry for the Carl Walther, the founder of the Walther company.
Rechnerlexikon has a page about Walther and separate pages for many models auch as the RMKZ 16, WSR 160, and others. The Walther material page includes lists of serial numbers.
Rechenmaschinen Illustrated has pictures and details of many Walther models.
John Wolff's Web Museum has a page about Walther.
Rechenkasten has various pages about Walther, though mostly about the electronic calculators.
Detlev Bölter has in his collection an EMKD and RKZ.
Rechnen ohne Strom has several Walther pinwheel machines.
XNumber has the article The Walther Company, Historic Recollections by Ray Mackay.
Christian-M. Hamann has an RK, a WSR-160, as well as a Diwa-32.
Vintage Calculators has a Muldivo Mentor with a nice explanation of the stationary input pins.
Cris vande Velde has a several Walther machines, such as RMK, EMKD, SMKZ, DMKZ, and WSR-110/160.

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