# Collection Overview

The present collection contains a total of 225 slide rules, with 209 linear slide rules, 11 circular rules, as well as 2 and 3 spiral and helical rules, respectively. The “rule” for entrance into the collection is that there must be a logarithmic scale as part of the device. Hence sectors and Gunter’s rules are eligible, for instance, though they are not technically “slide” rules. However, items such as Addiators, Curtas, and other mechanical computational tools are not included.

The following tables provide a short summary of the collection. As can be seen, the largest portion of the collection has been produced by three major manufacturers:

Maker Number in Collection
Keuffel & Esser 61 slide rules
Hemmi 32 slide rules
Pickett 27 slide rules
Dietzgen 13 slide rules
Faber/Faber-Castell 10 slide rules
Lawrence/Engineering Instruments 9 slide rules

As for the rest, the number of slide rules in the collection and their manufacturers are summarized here:

Number per Maker Makers
$$> 6$$ slide rules
6 slide rules Charvoz-Roos
5 slide rules Richardson, Sterling, noID
4 slide rules Aristo, Gilson, Nestler
3 slide rules Concise, Relay-Ricoh, Thornton
2 slide rules Acu-Rule, Festus, MARC, Otis King, Rietz
1 slide rule Alco, American Blueprint, Baetzmann, Blundell Rules Limited, Boykin, C-Thru, Davies, Factory10, Fearns Calculators, Fowler, Goodyear, HH, Jacob and Halse, KHH, MATSKU, Novotni, Reiss, Ruyi, Staedtler, Stanley, Unique

In the tables found in the following chapters, production dates for the slide rules are provided. Each date is at least a best guess, though some dates are fairly accurate based upon serial numbers or details of the particular slide rule.

• If the Year of the slide rule is fairly certain, through a serial number, date mark or other documented knowledge about the rule, then there will be a single year listed with no preceding “c.” (circa) in front of the date.
• If the Year is not certain but a narrow range of dates for a particular slide rule can be determined, then this range is provided in the Year column.
• Otherwise, a “c.” will precede the date in the Year column, signifying a guess with a much wider range of uncertainty.

Other information found in the tables includes:

• Typ = type of slide rule: L (linear), C (circular), S (spiral), H (helical)

• Mat = primary material used: wd (wood or bamboo), pl (plastic), ss (stainless), Al (Aluminum), Mg (Magnesium), iv (ivory), pp (paper)

• Size = length of the slide rule’s primary scale (e.g., “C”), in inches (total “path length” if circular, spiral, or helical slide rule)

• Serial = serial number or date stamp found on the slide rule