Keuffel & Esser Slide Rules

Probably my favourite slide rule manufacturer, K&E was the dominant slide rule maker in the US. They also made a large range of drafting and related products, and even had offices here in Montreal. Their rules featured mahogany cores with celluloid facings, and have one of the nicest "feels" among slide rules, if you know what I mean. My personal favourite (and considered one of the top three among collectors) is the K&E 4081 series with the exposed mahogany wood along the edges. Their high quality leather cases are also among the best, and were frequently imitated. Over the course of production, they carried an extensive range of slide rule models, although they frequently changed their model numbering schemes in the last couple of decades of slide rule production, confusing matters considerably for collectors. They eventually switched to all-plastic models, but continued their tradition for innovation in layout and scale design right up to the bitter end. Unfortunately they didn't survive intact, but their final assets were eventually acquired by the reproduction paper and film company Azon, which also bought out what was left of the Frederick Post and Hughes Owens companies. Where available, I've listed model variants in chronological order on this page. Please note that some of the estimated dates have undergone recent revision, thanks to Clark McCoy's excellent reference set of various K&E catalogs. Additional dating information has been obtained from a variety of sources, with special thanks to Ed Chamberlain for his excellent set of K&E dating curves based on K&E serial numbers.

K&E 4053-3

One of my favourite rules ... check out my Evolution of a Slide Rule page for an extensive look at all the different 4053's in my collection.

K&E 4058W (ca. 1950)

The 4058W was K&E's most basic offering. In fact, this was their "Beginners" model, and it was the most simply (and cheaply) made of any K&E rule. Like the more advanced 4053 series, this model also goes back a long way and underwent a number of design modifications over the years. This representative example from my collection is a fairly late model built, with an all-plastic spring-mounted cursor and mid-century table of equivalents on the back. Made apparently of light-weight pressed wood, this model has a simple white-painted face with printed monotone scales, very reminiscent of the inexpensive Lawrence Engineering rules. Unlike all other K&E rules, this model lacks parts/serial numbers, consistent with its basic design features. I've seen various types of paperboard/vinyl sleeves to protect the rule, and a decent enough model is shown in the high resolution scans. Judging from K&E's price list, this model rule would have retailed for $2.25 US in the early 1950's. I've also included a scan of a manual for this model rule, taken from the same time period (final copyright date 1944). This Beginners rule is just that ... basic, functional, with no pretension to being anything more.

K&E N4080-3 (ca. 1950)

The various 408x models are considered to be K&E's premiere slide rules. Made of celluloid on mahogany, they feature an excellent and extensive scale arrangement. As one fellow enthusiast noted, Pickett's may have gone to the moon, but these are the slide rules that probably built the bomb! The N designation ("New") was adopted in 1949 for this series of rules, and presumably reflects the major scale and label change at that time. However, K&E was not consistent in its use this label, and eventually dropped it on the 408x series around 1954. I'd estimate the age of this particular rule to 1950, based on Ed Chamberlain's reference set of dating curves for K&E serial numbers. The first difference you'll notice is that all of the rule's descriptive product information and bona fides on listed the edge instead of the face, as was standard on earlier model rules. You'll also notice that this model lacks the gorgeous relieved wood edges of later N specimens (earliest example I have with the inlaid wood is 1951). The only specific difference between the 4080-3 and 4081-3 series that I can see is in the trig scale arrangement (the 4081-3 is a decitrig).

All the later-build high-end duplex rules like this one also feature a revised cursor assembly that seems to have resolved the KERCS problem (K&E Rotting Cursor Syndrome) that affected many of the older model duplex rules. The new cursor end pieces are made out of a different sort of plastic that appears to be very resistant to age-related breakdown, and have remained ivory-white to this day. The K&E label and patent numbers are hard to see on these later-model cursors, as they are on the face pieces that are partially obscured by the metal frame. One little oddity about this particular rule: when I received it, I noticed that one of the pieces of cursor glass was actually a prosthetic replacement! Shown in its own scan, it appears to be a piece of Plexiglass crudely cut to fit the cursor frame. It also has two replacement hairlines etched in it - presumably the creator realized he had miscalculated once he had assembled his makeshift apparatus, and so etched a second line that accurately translated the cursor mark from the intact side. In any case, I've replaced it with an extra original 4081 cursor glass I had available ... good as new now. The manual that came with the rule has a final copyright date of 1948, so that is also consistent with the estimated age of this specimen. The case is the standard form-fitting cardboard type with leather closing flaps bolted on, although this particular specimen is in pretty bad shape. Please check out the remaining rules on this page for a detailed comparison.

K&E 4081-3 (ca. 1937)

This is the probably the oldest 4081-3 in my collection, dating back to the year it was first introduced (serial number places it to 1937). It shares many similar design features with the older 4091 and 4092 models further down this page. The rule has an excellent feel, and is made of celluloid covering a mahogany wood core. In fact, this rule has one the whitest patinas I've seen on a rule of this age ... most of the time the exposed surfaces have aged to a creamy yellow colour. Even the cursor end pieces (with a 1937 patent number) are in excellent condition and show no signs of breakdown. Like all the older model rules, the K&E product information and patent dates are on the face of the rule. Similar to the just slightly older 4091 rule further down this page, although now with a red DI scale on the back. Instead of the typical leather/cardboard cases shown with the other rules on this page, this one has the older hard textured particle-board type case with leather closing flaps bolted on. A nice early production model of this rule.

K&E 4081-3S (ca. 1938)

Another version of this classic slide rule ... it's interesting to see how quickly it started to change. In principle the same as the preceding model on this page, but with a couple of interesting differences. On the body of the rule, the LL0 and LL00 scales are now in red instead of black, and reversed in relative position. All the other scales and the K&E labels and patent dates have stayed the same. The manual is in excellent condition, with the pages still very white. This particular rule also features the high-end K&E all-leather orange coloured case with chamois-like interior. In fact, the "S" in the title refers to the label on the case, and presumably reflects the "stitched" all-leather case design. A nice rule that was obviously highly prized, as the name of the original owner (one James W. Smith) is imprinted in gold lettering on both the case and the rule. Looks like he got a lot of use out of it too!

K&E 4081-3S (ca. 1944)

Not much changed on this model in the early 40's ... except, oddly enough, the patent numbers! This rule, and others I've seen from the same time period, have additional late 30's patent numbers on the face. Otherwise, they are not appreciably different from the one shown immediately above. The leather case for this rule is also the high quality leather type, and it has aged to a nicely satisfying rich brown colour. Like with many high end slide rules, this particular rule seems to have gone through a number of owners, given the different name engraved on the rule and and the various ones imprinted or written in ink on the case. Overall, a well worn specimen of this rule ...

K&E N4081-3 (ca. 1951)

This is actually the first slide rule I ever bought, and still one of the nicest I've seen (although it desperately needs a cleaning, which I haven't gotten around to yet). It differs considerably in design and scale arrangement from its predecessors. The most obvious change is the relieved mahogany wood exposed on the edge pieces of the rule, along with the model and patent information. In terms of scale arrangement, the L and LL1 scales have moved to the back, and the LL02 and LL03 scales have moved to the front of the rule. An extra LL01 scale has also been added to the back, which has seen a major re-arrangement of scale locations along with the re-labelling of ST as SRT. They have also dropped the DI scale on the back, for some reason. This rule also features the more modern age-resistant cursor assembly seen on the N variants. I just can't say enough nice things about this design. These rules could well be considered the standard bearer of slide rules! For a comparison, you might want to check out my Dietzgen page for some competing similar models of the same time period. The case for this model is the standard form-fitting black cardboard with leather closing flaps bolted on. I've also included a scan with this model of the standard K&E product insert for duplex rules, telling you how to care for and adjust your rule (final copyright date 1949).

K&E 4081-3 (ca. 1958)

The final version of this rule under the original 4081 label, and my clear favourite. It is virtually identical the N4081-3 shown above, and is indisputably the nicest version of this model. The only obvious difference that I can is that they added the registered logo after the name LOG LOG DUPLEX DECITRIG (see the two high resolution edge scans). This particular rule is in near mint condition, as the original owner informs me it was only scarcely used in the early 60's and then carefully stored away. In fact, the rule has never been cleaned and still has its original luster and shine! Serial number places it to 1958 ... although I've also had a few rules dating to 1957 that were identical in every way to this one. The case is the high quality all-leather orange model with chamois interior, and is in immaculate condition aside from some slight wrinkling on the closing flap. I've never seen the insides of this type of case in such amazingly good condition. The manual that came with this rule has a final copyright date of 1955, confirming the switch back to the original notation without the "N" (I wish someone could explain that to me ...). In any case, as far as I am concerned, this is the most outstanding rule in my collection!

K&E 4083-3 (ca. 1946)

The K&E vector equivalent of the decitrig 4081. This rule is virtually identical to its close cousin of the same time period, with the replacement of the cubic and inverse D scales with Th, Sh2, and Sh1 scales on the backside. It has stator patent dates identical to the similar vintage model 4081-3S show previously on this page, and presumably shared a similar production run. Naturally, it is also lacking the relieved wood edges, which didn't come along until a bit later. The case is the older black textured particle-board type with bolted-on leather closing flap imprinted 4083-3 on the front and LOG LOG DUPLEX VECTOR on the hard edge on the leather. The case has also been subsequently imprinted with the former owner's name, Clarke & Stuart Co., Ltd., of Vancouver B.C. A beautiful rule, in excellent shape.

Update: Thanks to Dave Martindale, it seems that Clarke & Stuart was actually a distributor of K&E rules in that region. They certainly did a nice job of engraving their name on the case - certainly fooled me! I'm not sure of the time frame in which they sold K&E rules, but Dave informs me he has catalogs from the late 1940s that have their name printed on the cover. That would certainly fit in this rule's serial number and design features.

K&E 4083-3 (ca. 1954)

A somewhat rare fine ... the final version of the 4083-3 with relieved wood edges. Judging from the serial number, it is fairly late model build, circa 1954. You'll notice that they clearly seem to have dropped the N designation by this point. Like its contemporary non-vector siblings, it has undergone a considerable re-adjustment in the location of the log-log scales, and the inverted DI scale has returned. This particular rule was in pretty bad shape when I got it, but it cleaned up very nicely as you can see on the high resolution scans. Unfortunately, though, a strip of edge laminate is gone from the labelled edge. The case is the high quality orange leather variant, but is missing most of the closing flap (not an uncommon problem). What I can't understand is why these are so hard to find. It's such a great rule, I would have though K&E would have made more of them. Go figure!

K&E 4088-3S (ca. 1924)

An early model duplex slide rule, with the old frameless cursor design. Despite the small chip on the cursor, it is still in remarkable shape, and has the attractive all-leather case with chamois interior (fully stitched instead of partially bolted). It's very rare to find them in this condition today! Judging from the serial number, I'd date this rule to about 1924, which fits with the all-stitched early version of the high end leather case. The manual shown is actually one I picked up for a later 30's model rule, but the scale arrangement isn't appreciably different - just the scale font and cursor style changed with time. Interestingly, this rule is virtually identical to the contemporary Hemmi Hughes Owens 1765 in my collection (except in mahogany wood, in this case). That particular rule has taken quite a beating though ... check it out for a comparison. Interestingly, it's the only time I've seen such similar offerings from these two premiere slide rule companies.

K&E 4091-3S (ca. 1935)

An older version of K&E's high end duplex style vector rule, and a very interesting specimen! This rule clearly dates to 1935 on the basis of its serial number, but you'll notice the more modern cursor assembly. This improved cursor style is generally believed to have been introduced in 1936, according to entries in the K&E catalogs. And the vast majority of cursors contain a 1937 patent date printed on the end pieces ... but this is the second time I've managed to find one that simply says "patent pending" (the other is on my 4053-3 page, and that rule dates to 1934). This suggests to me that K&E actually released this cursor a couple of years earlier than 1936, but I'm not sure as yet to the dates. In terms of scale arrangement, notice the slightly reduced number of scales compared to the later 4083-3 (also a vector rule), and the inclusion of the identification labels on the back of the rule. Otherwise, not much changed from this immediate precursor ... even the name stayed the same (K&E Log Log Decitrig on the closing flap). The case is the standard high end leather case with chamois interior, but with one little oddity - it actually still has the belt attachment on the back! Would you believe that this is the K&E first rule I've come across that actually still has it? Rather hard to find. The rule and case are also both in very good condition ... a fascinating specimen, and a nice addition to the my K&E family.

K&E 4092-3 (ca. 1929)

An even older version of K&E's standard high end rule, although I must admit this one had me confused for awhile. Clearly, someone has gone and replaced the original frameless cursor with one manufactured after 1937. I'm not entirely surprised ... the older frameless design was prone to breaking. The serial number of this rule clearly places it to 1929, and that fits with patent date of April, 1924 on the face of the rule (later models just had patent numbers). The 4092-3 shares many of the same design features of the early models 4081's and the 4091 presented above. The main differences are the reduced number of scales on this rule, with their simpler monotone appearance and less intuitive layout as you might expected from an older rule. The case is also made of the older all-leather style, with the hinge pieces sewn on instead of bolted. Unfortunately most of the closing flap is missing, but you can still see the stitching in the high resolution pictures. I've also included a scan of the first page of a tattered set of instruction sheets for this model rule. Overall, still a nice mahogany/celluloid rule, sharing the same fundamental design as later rules. And as for the replacement parts, K&E clearly expected you to replace broken parts with newer versions ... it keeps the rules functional, but it does make things tricky for collectors!

K&E 4100 - Stadia (ca. 1962)

The 4100, also known as a Stadia rule, is a specialized surveyor's slide rule. The rule has the standard late model Mannheim body, similar to the last incarnation of my 4053-3 series. It features R, H, HC, V, and A scales on the face, with a B and C scales on the reverse of the slider, and inch and centimeter rulers along the edges. In case you're wondering what all those scales do, no problem - there's an explanation on how to use them inside the slide rule behind the slider! Basically, they refer to horizontal (H, HC) and vertical (V) distance, as well as elevation (A, B, R) ... everything the average surveyor would need to know. The back of the rule has the standard conversion factors. Interestingly, the face of the rule has yellowed considerably with age, whereas the solid plastic base remains ivory-white. Clearly K&E used a difference type of celluloid base for these two materials. The case is the standard form-fitting black cardboard type with leather closing flaps bolted on. A interesting (and rare) special purpose rule ... and obviously highly prized by collectors, given the insane amounts of money I've seen shelled out for these things on eBay!

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Page last updated on September 27, 2002 -
All material © 1999, 2001 by Eric Marcotte, Ph.D.