David Rance’s

Crib Sheet
for
Solving Slide Rule Mysteries

Besides a traditional Internet “Google search” some readily available and handy online tools can help track down a mysterious model or at least quickly provide clues to narrow down its possible origin.

Bulk searches

Look for some uncommon or out of the ordinary text incised or printed anywhere on the mystery model. For example, this could be a name, a number combination, a place, an address, some distinctive text in a table on the back of the stock, etc. Use an unusual construction or combination of words and/or numbers to search:

1. Net Search
   This search option developed by Rod Lovett searches an extensive Links Library of slide rule–related websites.
   
2. ISRM Search
   Mike Konshak’s International Slide Rule Museum (ISRM) houses many, many highly descriptive galleries containing a plethora of calculating aids. The inbuilt search option checks the whole website for possible “hits”.
   
3. Herman’s Archive
   Rod Lovett’s online option for searching legendary late Dutch collector Herman van Herwijnen’s lifetime work of over 5000 catalogued slide rules and other calculating aids he published in his “Blue Book” and later CD version.
   
4. Archive of Collections
   This ongoing development between Rod Lovett and the Oughtred Society aims to publish and preserve online the more impressive collections of OS members. An all-inclusive option searches the complete current contents of the entire archive.

Reversed image searches

Try this image!

Crop a high-resolution image of any mystery model to highlight some uncommon or unusual part of the construction or layout. Use this to do a reverse Google image search .
Searching trade marks by image can be done in TMview or the “Brand Logo” section of the WIPO Global Brand database.

Scales and scale layouts

For unbranded or OEM made slide rules the style of the commonly found π gauge mark common to many standard scales can reveal its hidden provenance. Jim Bready’s 2022 updated version of his original 2002 “Mystery Slide Rules” article published in the autumn edition 31 of the JOS shows, among other tips, the recognisable different styles of π used by various makers.

Searching for a common scale layout like a Rietz or a Darmstadt on any mystery rule is largely pointless. However, if say all the Rietz scales are uncommonly placed on the front face of the stock instead of the Trig scales being on the back of the slide or there is an unusual combination or ordering of some of the scales, a targeted search can help. A little-known feature of Rod Lovett’s online option for searching Herman’s Archive is a targeted search restricted to just the scale layout. To activate this feature the search criteria have to be preceded by “#s”. Any scales in the search criteria also have to reflect the coding style adopted by Herman for his Archive and exactly follow the order that the scales appear on the slide rule — e.g. a search with “#s T K A = B CI C = D L S ST” will surprisingly return just a few hits.

Instructions

Sadly apart from the language they are published in, unbranded instruction sheets or booklets rarely give much away. However, the contents of any colophon or details printed in a small font at the bottom of the page (often the back page) may provide some maker country or location clues.

Boxes and cases

Over time the originally supplied slide rule packaging often gets lost. If not lost, any unbranded but original boxes or cases may, on closer inspection, harbour some hidden clues. It is often difficult to see but many makers blind-stamped their “unmarked” boxes or cases with secret or hidden identification marks. Peter Hopp’s 2016 updated version of his original 2000 “Slide Rule Box Identification Marks” article published in the Colin Barnes memorial edition of the Gazette shows how to spot and identify such marks.

Do you use a tool for slide rule research which is not described here? Please let us know at @