Keuffel & Esser

K&E made some of the best slide rules. They were accurate, looked good, and worked well.

K&E 4080-3

This was my Dad's, Jim Wolfson's, slide rule at NYU. The case is beautifully stenciled "J.W. '44", and the rule probably dates to 1940. He used this for 30 years as an engineer, first in aeronautics where he worked for Charles Lindberg, and later as a refinery designer in the petroleum Industry. He used it to show me how a slide rule worked.

K&E 4083-3

Another beautiful K&E rule, bearing hyperboic sine (Sh1, Sh2) and tangent (Th) scales for electrical engineers. This one bears the SRT scale (radian sine & tangent), which first appears in a September 1955 revision of the K&E manual. It also has a low serial number, 032215, which suggests manufacture shortly after K&E rolled over serial numbers in 1955.

I love the way the edges of this rule are constructed - exposed wood with a plastic inlay. On the top edge, the inlay is inscribed with the model number, name, etc.

K&E N4081-3

This nice rule arrived in rough shape: the cursor had crumbled and rusted, and left a stain on the rule. But after I made new blocks for the cursor and gave the rule a good cleaning, it's back in good form.

K&E 4181-1 (68-1282)

This 6" rule cost $10 in 1962. Engineers walked around with these clipped to their breast pockets back then.

K&E 4187S (68-2047) Manual

K&E 4041 - 1903-1907

This is a basic "Mannheim" rule - just the A,B,C and D scales - but it's beautifully built like all of K&E's high end instruments.

The label in the case says "W.A. Young, MIT '07, 356 Mass Ave." (A small "WAY" is also gently inscribed into the wood on the back.) Assuming "'07" was engineer Young's class year, it suggests the rule dates to 1904-1907. Interestingly, the fabric-wrapped cardstock case has no labeling, and the bottom of the cursor is imprinted "PAT.APPL'FOR". These features suggest the earlier date to me.

K&E 4041 - 1914/15

K&E introduced a frameless cursor around 1914-15, and initially mounted the cursor on metal blocks. They switched to using celluloid blocks by 1916, probably due to costs, but possibly also because those two hunks of metal add a lot of weight to an otherwise light instrument. The rule features a table of formulas, constants and conversion factors on the reverse, exactly like the 1922 model below.

K&E 4041 - 1916-1921

This 4041 has the celluloid cursor blocks that replaced the metal ones in 1914-1915 model (above), and it doesn't have a serial number so it has to antedate the 1922 model below. Beyond that, I can't place the date.

K&E 4041 - 1922

I got this from a friend whose young son had gotten hold of it and somewhere lost the cursor. It should have an all-glass cursor. Thanks to Clark McCoy, you can see what this rule looks like when outfitted with the proper cursor. But even without it, it's a nice old rule.

We know this rule dates to 1922 because of an odd feature. Before 1922, K&E stamped the left ends of both the slide and stator with short 2-3 char codes that could be used to keep the parts together during manufacturing. But in 1922 they started printing matching 6 digit serial numbers on both parts instead. What's odd about this rule is that it has short codes on the ends of the parts, as well as serial number 17862 - but only on the slide. This strongly suggests it represents a transitional form.

Note in this version, as versus the earlier rule above, the addition of A,B,C,D scale labels at the left edge, and the repositioning of the red K&E, patent date, and made-in text.

K&E N4041 - 1925?

The serial number on this N4041, 112404, dates it to around 1925. It's very similar to the 4041 above, but the changes are interesting as shown in these photos (the earlier 40401 is on the on the top).

First, it is overall wider, 28mm instead of 25, with the extra space allocated a bigger slide with a large gap between the B and C scales on the slide. This matches the size of the 4053, so maybe K&E was able to save money by having one construction size that they simply equipped with different scales for the two models.

By this time K&E had started putting serial numbers on both the slide and stator, but as a consequence they had to steal 1cm from the ruler on the front edge. I guess for symmetry, they gave up the last centimeter, too.

On the reverse side, everything about the label is the same, but the log scale has been modified. Not only does it now have the "L" label, it runs from left-to-right instead of right-to-left.

K&E - N4041 - 1940?

K&E tweaked their rules quite a lot over the years. These photos show an N4041 from around 1940 (per its serial number 768490) as versus the 1925-ish rule from above (shown at the top of each photo).

In 1936 K&E started using a thin frame to secure the glass cursor to the blocks. Around 1930 they seem to have switched from a serif font to a sans-serif font for the scale labels. They also swapped the red K&E text with the patent text. The label on the rear was vastly changed in 1927-28. And, the L scale was modified to specify the range 0 to 1 instead of 0 to 10 some time between 1934 and 1940..

K&E 4041 Family Photo

Just for fun, this picture shows 4 of the above 4041 variants from earlier (top) to later (bottom). They're the 1914-15, 1922, 1925 and 1940 versions.

K&E 4053-3

This is like the 4041 above, but K&E added a CI scale on the slide and a K scale, cleverly located on the bottom edge. This rule was produced before K&E started using serial numbers in 1922.

Metal-framed cursors were discontinued in 1915, so it's earlier than that, too.

K&E N4053-3

K&E tweaked the design of the 4053-3, above, moving the K scale onto the bottom of the stator and employing a better cursor. From its serial number, 374487, it can be dated to 1948-9.

K&E N4053-5

A double-length version of the 4053. Pulling this from its case is like drawing a sword from its scabbard. You could call it ungainly, but it had advantages.

On the usual rule, the high end of the C/D scales gives tic marks in .05 increments: 9.05, 9.1, 9.15, 9.2, etc. You can't really tell the difference between an answer of 9.02 and 9.03.

On the double length rule there's room for 0.02 increments: 9.02, 9.04, 9.06, 9.08, 9.1, etc., allowing you to reasonably get accurate answers to 3 full significant digits.

K&E 4058C Beginner's Slide Rule

This model is all wood. Instead of inscribing the scales on celluloid laminated to wood, here the scales are inscribed directly on the wood itself.

The downside is that reading the scales is harder on the eyes, but the upside was a much cheaper instrument. For example, in 1941

this rule sold for only $1 while a 4041 went for $6.50. (That's about $15 vs. $100 in today's money!)

4185C Magnifier

If you want more precision and can't make the scale longer, make the light longer. I think there are more varied designs of magnifiers than of slide rules.

This one is pretty simple: it easily slips on or off the existing cursor of a 4080 rule. It provides a magnification of about 1.5 times as illustrated in the big closeup.

The green arrow is the un-magnified distance from 1.95 to 2.06 and the red arrow is the magnified distance. When viewed side-by-side, you can see that the red arrow is about 1.5 times longer than the green one.

K&E GP12 Manual

Now that I have the manual, I guess I need to collect a GP12 rule!