International Online Slide Rule Workshops Internationale Online Rekenlinialenworkshops

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.
The second online workshop was held in June 2025.
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 Online Rekenlinialenworkshops.
geeft aan welke items zijn besproken tijdens de eerste workshop in februari 2025.
De tweede online workshop heeft plaatsgevonden op zondag 15 juni 2025.
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 @

Filter: ⁄ ⁄

Logarex Typ01 Nathan Zeldes
We know the maker but nothing else – and it is a VERY weird design (look at the back too).
The “Pose-Marre” pen slide rule Nathan Zeldes
We have the “Gebrauchsmuster” but no other information about who manufactured it.
The 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.
Kawamura'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 ?
“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.
An 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?
“HH” Wooden slide rule Chris Hakkaart
Question:
1. What is “HH”?
Plastic slide rule Chris Hakkaart
Question:
1. Any idea?
Two slide rules with special figure Chris Hakkaart
Questions:
1. What does the special figure mean?
2. Name?
Simple slide rule with no name Chris Hakkaart
Question:
1. Name?
Folded plastic with plastic slide Chris Hakkaart
Question:
1. Name?
2. Purpose of small bulge at each side?
D&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?
“Ich Dien” slide rule Peter Hopp
Arranged by S. Waddington, Barnsley.
Questions:
1. ???
Nestler slide rule Jean Paul Hild
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
I 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 ?
German silver slide rule James Bready
Question:
1. ???
Four-slide slide rule Amy Ackerberg-Hastings
National Museum of American History, Catalog Number 1999.0068.01
Question:
1. What is this?
  Looks like some test score averager used in education. Peter Hopp
  The formula for computing grade point average is GPA = sum(class GPA * class credit hours) / sum(class credit hours). The Ones index can be positioned opposite the number of class credit hours for which a GPA of 1 was scored. Next, the Twos index can be positioned opposite the number of class hours for which a GPA of 2 was scored, etc. The sum of these products is then read on the fixed linear scale in the center of the rule.
  There is a gauge mark on the top edge of the bottom slide, just above the 2.6 mark of the scale on the lower edge of the same slide. By positioning the gauge mark opposite the earlier computed sum on the log scale with the range 10 to 240, the GPA (Grade Point Average) can be read on the lower scale of the slide opposite the total class credit hours on the bottom fixed scale. Eamonn Gormley
Japanese Artillery Simplex Slide Rule Amy Ackerberg-Hastings
National Museum of American History, Catalog Number 1978.2289.01.
Note: The PowerHouse Museum link should read https://collection.powerhouse.com.au/object/384855
Question:
1. Maker ?
Unknown Soho found in Germany Fred Astren
Question:
1. What is this?
Metal slide rule marked G. Atkins, London Roberto Pascual
Question:
1. ????
Unknown slide rule “H-P-S” via Jacques Perregaux
Question:
1. Maker?
2. What are the trio's of cursor hairlines used for?
MOUZIN 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?
4 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?
Slide 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?
Faber 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?
Cross 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.
Gilson 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?
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?
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?
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?
Calculating device João Roberto Gabbardo
Manufactured in Portugal on September 7, 1948.
Questions:
1. What are the scales for?
2. How do I use them?
Aristo 80144 João Roberto Gabbardo
For use in machining with a mechanical lathe.
Question:
1. How to use it?
Slide 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?
Aristo 10174 Paulo Rios
Question:
1. What is this cursor mark used for?
Reiss Artillery Andreas Poschinger
Question:
1. What do the gaugemarks M 42,7m and H 2,133m represent?
Pickett 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?
Mechanical Engineer Peter Hopp
Questions:
1. (Rare) product, prototype or home–made?
2. Should it be cleaned further?