International Workshops for slide rule collectors Internationale Workshops voor Rekenlinialenverzamelaars

Dutch Circle of Slide Rule Collectors Kring Historische Rekeninstrumenten

This page lists pictures of mysterious slide rules contributed to the International Online Slide Rule Workshops.
indicates items discussed during the first workshop, in February 2025.
indicates items discussed during the second workshop, in June 2025.
indicates items discussed during the third workshop, in December 2025.
The fourth International Workshop will be held on Sunday March 1, 2026, at 18:00 CET (17:00 UTC).
indicates that the mystery has been (almost) solved.
Click the items for more images, a complete description, questions and hopefully some answers.
But usually there is no definitive answer to the questions!
If you like to add an answer, or suggest an item for the next discussion, please send a message to @ Deze pagina toont afbeeldingen van mysterieuze rekenlinialen die zijn aangemeld voor de Internationale Workshops voor rekenlinialenverzamelaars.
geeft aan welke items zijn besproken tijdens de eerste workshop in februari 2025.
geeft aan welke items zijn besproken tijdens de eerste workshop in juni 2025.
geeft aan welke items zijn besproken tijdens de derde workshop in december 2025.
De vierde International Workshop zal plaatsvinden op Zondag 1 maart 2026, om 18:00 MET.
betekent dat het mysterie (zo goed als) opgelost is.
Klik op de items voor meer plaatjes, en volledige beschrijving, vragen en mogelijke antwoorden.
Maar meestal is er nog geen definitief antwoord op de gestelde vragen!
Als u een antwoord heeft, of een item voor een volgende workshop wil suggereren, stuur dan een mailtje dan naar @

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  1. Hoh und HahneHoh & Hahne, probably Nestler Wolfgang Bode
    Question:
    1. What were the A and B Scales used for?
  2. Russian made slide rule25 cm long slide rule, Russian made D. Lehn Hilton
    Question:
    1. Manufacturer, date, target market, etc.
  3. Made in USA slide rule12.5 cm long slide rule with only “Made in U.S.A.” on the face D. Lehn Hilton
    Question:
    1. Manufacturer, date, target market, etc.
  4. Germany slide rule10 cm long slide rule with only the word “Germany” in the right hand end of the valley D. Lehn Hilton
    Question:
    1. Manufacturer, date, target market, etc.
  5. slide ruleSlide rule with “PD1” logo and marked “Survey of Egypt” Peter Hopp
    Question:
    1. Can anyone throw any light on this, either logo or whatever?
  6. Speedy Calculator (Tesseract)“Speedy Calculator” Eamonn Gormley
    Questions:
    1. Manufacturer?
    2. When it was made?
    3. etc.
  7. ARISTO clonesLooking for clones of ARISTO school slide rules Karl Kleine
    Questions:
    1. Do you have any such ARISTO clones or have information about them?
    2. What brands, model numbers and names are used?
    3. In which countries / regions are particular models / brands sold?
    4. Do you have any information about prices, in particular relative to ARISTO originals?
    5. Do you know when these rules were made / sold?
    6. Have you seen clone variants, which are close copies of ARISTOs with some differences in the scales?
    7. Can you provide any pictures, of own specimen, from ebay etc offers, web sites, any other source?
  8. WichmannWichmann electrical slide rule with side wheels Heinz Mayr
    Questions:
    1. Who built this slide rule ?
    2. When ?
    3. Are there other examples ?
  9. FLARO260 × 40 mm cardboard slide rule marked FLARO and Rothmann Leo van der Lucht
    Questions:
    1. Has anyone seen anything like this before?
    2. Does anyone know FLARO or the name Rothmann?
    3. Could this be a model for further production?
  10. Proportion Rule18-inch proportions/type-setting rule Mike Syphers
    Questions:
    1. Who was the maker?
    2. What year? (perhaps 1940/50s) ?
  11. 20 inch Hemmi20-inch Hemmi, with off-centered rear window; special scale arrangement Mike Syphers
    Questions:
    1. Does this have a proper name or model number?
    2. What was its purpose; perhaps miltary, aerial photography?
  12. Textile?One-sided, three stators and three slides, and a multitude of hand-drawn scales Nathan Zeldes
    Questions:
    1. Who made it?
    2. What purpose?
  13. Didier StettinDennert & Pape Didier-Stettin Keramik slide rule FanHsiu
    Question:
    1. What is the function of the A1, A2, S1 and S2 scales?
  14. Nestler side cursorNestler Paulo Rios
    Questions:
    1. Is this a NESTLER 27 Präzision?
    2. What can we tell about the manufacturing date?
  15. Decisions of the Treasury DepartmentEngineers' slide rule from 1893 with paper scales on the cylinder and cross bar Andries de Man
    Questions:
    1. Which slide rule is described here?
    2. Does anyone have an 1893 L. Manasse instruments catalog?
  16. Soviet slide rule with pinSoviet-LFAI Aviation Navigator's slide rule with 2 pins on the slide. Chris Hakkaart
    Questions:
    1. How to use scales on this slide rule?
    2. What is the function of the 2 pins?
  17. 20 cm plastic20 cm plastic slide rule “NO.83” with formulas and conversion tables in English. Wolfgang Bode
    Questions:
    1. Who knows the manufacturer?
    2. How old could this be?
  18. Fuller in boxFuller with detachable handle Bart Depuydt
    Question:
    1. Are there any other Fullers with a detachable handle, apart from Barnard's Coordinate Spiral Slide Rule ?
  19. J. Hemmi 82J. Hemmi 82 Pocket Bart Depuydt
    Question:
    1. Why do the slots on the back differ from all Hemmi's shown in the ISRM ?
  20. 9 inch Gunter9 inch Gunter Bart Depuydt
    Questions:
    1. Gunters are usually 1 foot or 2 feet long. Are other 9 inch Gunter rules known?
    2. Why is there no “Line of Numbers” or NUM scale?
    3. What is the I*M scale ?
    4. What is the HOU scale ?
  21. A & CA&C pocket slide rule with a wooden core and Celluloid surfaces Jacques Perregaux
    Question:
    1. Maker?
  22. Mechanical EngineerMechanical Engineer Peter Hopp
    Questions:
    1. (Rare) product, prototype or home–made?
    2. Should it be cleaned further?
  23. Pickett PocketsPickett Pocket slide rules Eric Rinehart
    The development chronology of Pickett Pocket-size slide rules is not as well described as that of Pickett full-size slide rules. (Roger Shepherd, Thomas Croxton)
    Questions:
    1. Do those features of the pocket rules coincide with those of the full-size rules?
    2. Did the pocket rules change from magnesium alloy to aluminum alloy at the same time as the full-size rules?
    3. Did the pocket rules change from metal cursor bars to plastic at the same time?
    4. Can anyone give more information or a timeline about the "hooked" stator posts on some pocket rules?
  24. Sistema de MedeirosReiss Artillery Andreas Poschinger
    Question:
    1. What do the gaugemarks M 42,7m and H 2,133m represent?
  25. Aristo 10174Aristo 10174 Paulo Rios
    Question:
    1. What is this cursor mark used for?
  26. Sistema de MedeirosSlide rule Paulo Rios
    “Sistema de Medeiros” slide rule made by the Brazilian factory of technical drawing materials Arquimedes. No cursor, no documentation.
    Questions:
    1. What should the cursor look like, so it can be reconstructed?
    2. What is this? How to use it?
  27. Aristo 80144Aristo 80144 João Roberto Gabbardo
    For use in machining with a mechanical lathe.
    Question:
    1. How to use it?
  28. Portugal made calculating deviceCalculating device João Roberto Gabbardo
    Manufactured in Portugal on September 7, 1948.
    Questions:
    1. What are the scales for?
    2. How do I use them?
  29. Brazil made pocket slide rule Pocket slide rule João Roberto Gabbardo
    Type of Electro slide rule made by the Brazilian factory of technical drawing materials Arquimedes.
    Questions:
    1. Is it really an Electro slide rule?
    2. Why are there 6 trigonometric scales?
    3. What is the purpose of the “phi 0” scale?
    4. How do you use the scales?
  30. Brazil made circular slide rule Circular slide rule with two overlapping discs João Roberto Gabbardo
    The upper disc is transparent and has a hairline and also a D scale. Made in Brazil to be distributed as a company gift.
    Question:
    1. Why was this construction chosen?
  31. Brazil made CC Moller Line Loss and Voltage Drop Calculator Copy of the CC Moller Line Loss and Voltage Drop Calculator João Roberto Gabbardo
    Made in Brazil, the original texts were translated into Brazilian Portuguese.
    Question:
    1. What is the date of manufacture?
  32. Gilson Bearing AveragerGilson Bearing AveragerJohn Runnels
    Manufactured for the U.S. Navy. It has a mechanical linkage that finds the midway point between two compass bearings. Not a weighted average, just the midpoint. Also, the range of allowed inputs is limited.
    Questions:
    1. What was the purpose of this device?
    2. What would be the purpose of a device that only calculates a simple, unweighted average of two numbers, and only over a limited range?
  33. cross sectionsCross sections, stiffener Chris Hakkaart
    Questions:
    1. Who can explain more ins and outs of the stiffeners used by the different manufacturers?
    2. Was plastic stiffener used for printing numbers, or was it (also?) used for stiffening. In this case is the thin sheet op plastic stiffer than the thicker mahogany? Who knows more about this subject.
    3. Does somebody has data (bending) about the effect of the (metal) strips? Is the slide rule really stiffer?
    4. Some slide rules have screws. Was that really an improvement? Are data available?
    5. Do you know of other ways or other purposes the strip was used?
    6. If there are no data available about the improvement of the different types and directions of stiffeners, is somebody in the audience willing and capable of doing bending tests? You need to have or to set up some testing facility for it. It would be nice if we — as collectors — can qualitatively provide testing results.
  34. Faber Castell rulerFaber Castell drawing ruler with metal strips Chris Hakkaart
    Questions:
    1. Do you know other manufacturers of drawing rulers who have done similar?
    2. The type of timber is not known. Do you have any idea? Boxwood? Mahogany?
  35. veneer slide ruleSlide rule made of thin layers of timber, pressed and glued together Chris Hakkaart
    Questions:
    1. Has anybody an example of such a Faber Castell or another brand which used the same technique?
    2. Does somebody know the FC number of this type of slide rule?
    3. A slide rule is about say 5 mm thick. Veneer is about 1 mm thick. So what problem solves the several layers of thin timber?
    4. Is this a cheaper method of production?
    5. Any idea what the advantages are?
    6. Any idea in what year this type of construction was used/ was started?
  36. 4 sided English slide rule4 sided English slide rule Chris Hakkaart
    Questions:
    1. Which type of wood is used for my 4 sided English slide rule? Is this Boxwood?
    2. But why has the inside of my slide rule a very light color, compared with the outside?
  37. MOUZIN slide ruleMOUZIN slide rule Chris Hakkaart
    Questions:
    1. Who has a MOUZIN in his/her collection? Can you show it during the WORKSHOP!
    2. Type of metal?
  38. Unknown slide rule H-P-SUnknown slide rule “H-P-S” via Jacques Perregaux
    Question:
    1. Maker?
    2. What are the trio's of cursor hairlines used for?
  39. Metal slide rule G. AtkinsMetal slide rule marked G. Atkins, London Roberto Pascual
    Question:
    1. ????
  40. German SOHO?Unknown Soho found in Germany Fred Astren
    Question:
    1. What is this?
  41. Catalog Number 1978.2289.01Japanese Artillery Simplex Slide Rule Amy Ackerberg-Hastings
    National Museum of American History, Catalog Number 1978.2289.01.
    Question:
    1. Maker ?
  42. Catalog Number: 1999.0068.01Four-slide slide rule Amy Ackerberg-Hastings
    National Museum of American History, Catalog Number 1999.0068.01
    Question:
    1. What is this?
  43. German silverGerman silver slide rule James Bready
    Question:
    1. ???
  44. I of CI of C slide rule Jean Paul Hild
    Questions:
    1. Who made it ?
    2. Where was it made ?
    3. What did it serve for ?
    4. How does it work ?
    5. What is the purpose of the two windows in the bottom ?
  45. NestlerNestler slide rule Jean Paul Hild
    Questions:
    1. When was it manufactured ?
      Seems to be of SOHO type but I couln'd find other Soho rules from Nestler.
    2. Why are the scales deferred ? (see picture)
      Andreas Faßbender has provided an extensive report
  46. Ich Dien“Ich Dien” slide rule Peter Hopp
    Arranged by S. Waddington, Barnsley.
    Questions:
    1. ???
  47. DP slide rule with db, μv and MHzD&P slide rule with db, μv and MHz scales. Nikos Velissaris
    It is made of plastic and dated probably around 1935 or 1936.
    Questions:
    1. What is it used for?
    2. When was it made?
  48. bulgeFolded plastic with plastic slide Chris Hakkaart
    Question:
    1. Name?
    2. Purpose of small bulge at each side?
  49. Slide rule data slipsSimple slide rule with no name Chris Hakkaart
    Question:
    1. Name?
  50. Special markingTwo slide rules with special figure Chris Hakkaart
    Questions:
    1. What does the special figure mean?
    2. Name?
  51. Plastic slide rulePlastic slide rule Chris Hakkaart
    Question:
    1. Any idea?
  52. HH“HH” Wooden slide rule Chris Hakkaart
    Question:
    1. What is “HH”?
  53. black discAn unknown black disc. Leo van der Lucht
    Questions:
    1. What is this disk for?
    2. How does this disk work?
    3. Can a manufacturer be identified?
  54. Zelluglas“Zelluglas” slide rule Leo van der Lucht
    Questions:
    1. Has anyone ever seen this slide rule? It makes me suspect that it comes from German-speaking country because of the descriptions on the back
    2. Who made it? “Zelluglas” is not found as information in relation to slide rules.
  55. KawamuraKawamura's Position Line Calculator” John Mann
    Questions:
    1. Where and when was it made?
    2. Which company made it?
    3. How to use it: what are “h”, “d”, “l” what do the answers mean?
    4. Why are there more scales on this than on the D&P HR1 ?
  56. EngPenThe EngPen Nathan Zeldes
    We know really nothing about this pencil slide rule, except for US patent 883800 granted to William Harlow, which describes an instrument that is not completely identical to this one.
  57. Pose MarreThe “Pose-Marre” pen slide rule Nathan Zeldes
    We have the “Gebrauchsmuster” but no other information about who manufactured it.
  58. Logarex01Logarex Typ01 Nathan Zeldes
    We know the maker but nothing else – and it is a VERY weird design (look at the back too).
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