Slide Rules!

Last Updated: 7/9/15
N902-ES demonstration rule added.

My Slide Rules

    After some eBay purchases in 2001, my collection swelled again, so I decided to rearrange the gallery by type rather than chronological order. I'm splitting it into five categories: short rules (pocket or speed rules), long rules (standard straight rules), circular rules, unusual rules and then have the various metric converter rules at the end. At some point I really need to go back and take new pictures of some of these, there's 20-year-old scans of some.

Short Rules

Post Model 1444K

    Normal position. The center stick is reversible, with B, CI and C scales on the main side and S, L and T on the back (see below). A, D and K are the fixed scales. Made from laminated bamboo.

    It's worth noting that moving the L scale to the sliding stick requires that it be flipped, reading from right to left instead of the normal left to right. I'm also told that the windows on the back of the rule can be used for this without flipping the stick, but am still working out how to read it this way.
    This was the first rule I got. I'm not sure if I found it in my grandpa's basement or at a clearance store, but I know I was about 14-15 when I got it and started to try and puzzle it out.

Pickett Log Log Speed Rule Model N600-T

    A fine aluminum slide rule from Pickett, this one has scales A, B, C, CF (from pi to pi), CI, D, DF, DI, K, L, Ln, LL1, LL2, LL3, S, ST and T. Scanned slightly enlarged, it's six inches long and comes with a leather scabbard. The scabbard has a clever pull tab to bring the rule out far enough to grab easily. I also got the manual (my first!), which is an excellent example of a bad Thorndykian textbook...impenetrable prose followed by lots of drill exercises. I acquired this one from a friend, who had it sitting around in storage. When I showed him my N-515 (see long rules), he remembered having this one.

Pickett N400 Business Rule

    Another of Pickett's fine alumnimum rules, this one has the standard A, B, C, D, CI, K and L scales on one side. On the other, however, it has several scales intended for the businessman or shopkeeper, including the C% and R% scales for calculating percentages (percent increase, percent discount). Comes in the same sort of nifty scabbard as the N600.

Unis celluloid pocket rule

    Purchased on eBay. It's copyright to a French company, but was produced under license in Schenectady NY and sold in Chicago. The celluloid plastic has yellowed significantly. Not shown on the back is a centimeter scale ruler.

Long Rules

Acu-Math Model 400

    I sort of permanently "borrowed" this one from my father before heading off to graduate school. It's 12.25 inches long, and has the same scales as the Post, but with the more standard setup of S, L and T scales fixed. Made of plastic. Came with a leather scabbard.

Pickett Electronic Slide Rule Model N-515-T

    The image above shows the ends scanned at greater resolution, with the whole foot-long slide rule scanned at reduced size. This aluminum slide rule does not contain electronics, it's for use in electronics, so it has special scales for finding frequencies and so forth. It has A, B, C, CI, D, L, Ln, S and T scales, plus two more scales for dealing with electrical formulae (2 pi and H scales). Comes in a leather-covered hard plastic scabbard.

    This shot of the back of the N515T shows one of the scales used for figuring out orders of magnitude. Normally, a slide rule can't give you the order of magnitude of your answer, but this setup allowed engineers to find the magnitude of results from specific equations. You can also see a bit of the "cheat sheet" that covers most of the back of the rule. While all slide rules are reminders of a time gone past, things like listing wavelengths in feet and frequencies in Megacycles (rather than Megahertz) further place this rule in the past.
    I got this rule from Dave Crate in exchange for listing his page on mine (since, due tot he age of my page, it had good search engine penetration), and it really kicked off my serious acquisition of slide rules, between my showing the rule around and the attention I got from a newspaper piece soon after.

Aristo Nr.966

    Slightly larger than the Engineer's Metric Converter, this rule is by a company I'd not heard of before (made in Germany by Dennert & Pape), although I've since seen plenty of Aristo rules. On the side scanned, it has C, CF, CI, CIF, D, DF, K and L scales. On the other side are A, B, C, LL0, LL1, LL2, LL3, S and T. It comes in a slim box that is capped at one end.
    Acquired as part of the "Walker Collection," a batch of slide rules I got all at once when my appearance in the newspaper caused a woman to recall her husband's slide rule collection and decide that I might appreciate it.

Aristo Nr.970

    My second Aristo rule, this one apparently manufactured in Germany by Charvoz. It was a going-away gift from Dr. Benenson, one of my bosses during the two years I worked at Michigan State University's Lyman Briggs School, it was his first slide rule in high school/college. The front side (top half of the image) has K, A, B, T, ST, S, C, D, DI and LL0 scales. The back side has LL01, LL02, LL03, DF, CF, CIF, L, CI, D, LL1, LL2, LL3 scales. The rule's a bit longer than my current scanner, so the ends were cut off. The front side has raised "bumpers" at each end that connect the fixed parts together. On the right side of each scale is the mathematical operation for that scale. "DBGM" is printed on the back of the cursor and the front right end of the center stick, unsure what it means. (Update: Holger Petersen tells me it's short for Deutsches Bundes-Gebrauchsmuster, or "German Federal Utility Model." So, made either for government work, or to a set of government specifications.) The cursor itself is two plates of clear plastic spaced apart by aluminum top and bottom pieces. It has a Watts to Horsepower conversion on the front, and two more hairlines on the cursor whose purpose I haven't figured out yet. The one on the A/B scale has a separation that represents a multiple of about 1.28, and the one on the CD scale a multiple of 1.13. Going from the A/B to the C/D multiplies by 1.274 and then takes the square root. Huh. Came in a hard leather scabbard.

    Thanks to Stefan Vorkoetter for explaining some of the mysterious gauge lines. This site has more on them in general, and 1.28 bit above is 4/pi, with 1.13 useful for calculating the volume of a cylinder. Another of the lines lets you convert radius to area for a circle: place the main hairline on the radius on the A scale, and the other line will show the area on the D scale.

Pickett Microline 80

    A very cheap student rule made by Pickett, with A, B, C, D, CI, K, L, S and T scales. One-sided. Traded one of several Microline 120s I got in the wake of the newspaper article for this.

Pickett Microline 120

    A fairly basic one-sided plastic rule, with A, B, C, D, CI, K, L, S and T scales. Cheaply made, the center stick doesn't always line up when flush against the ends of the rule, but it can be used for basic learning and so forth. I got a bunch of rules from a man near town in the wake of being in the newspaper, and three of this rule came as part of the deal.
    I have since also acquired a yellow version of this (not scanned), which used to be the official "loaner" rule for Engineering Physics 2 at Kansas State University. And I use it occasionally for that purpose, to encourage students to remember their calculators....

Pickett N-902-ES

    A 2001 eBay purchase, this is a fairly simple trig rule, but it came with all the packaging and paperwork, including the warranty card. Not shown is the back of the rule, which has a sort of cheat-sheet for operation of the rule. Page down a bit to see the classroom demonstration version I acquired in 2015.

Lawrence Engineering Service 10-B

    This rule actually came as part of a book entitled The Slide Rule And How To Use It, published by Grosset and Dunlap in 1942. It's a workbook with a small box glued to the inside front cover containing the rule pictured above. It's a very basic learning rule, with only A, B, C, D, CI and K scales on a rather cheap painted softwood. The back has a number of conversion tables and useful information (such as the weight of a cubic inch of "wrot" iron). One interesting feature is the cylindrical magnifier over the center of the cursor.
    I got this as part of the same deal that included the 120s. However, I have since seen eBay infested with these cheap rules, often advertised as "Antique Wooden Slide Rule!" Hard to get more bottom of the line than the Lawrence rules, tho.

Pedigree Precision Rule

    But you can certainly try. Still in original packaging, this sold for $1.37 back in the day. Extremely basic, only A, B, C, CI, D, and K scales.

Sterling DeciTrig Log-Log

    A very nice two-sided long plastic rule, complete with mathematical notation (as on the Pickett N-515T) to explain the use of the rule. Has scales: A, B, C, CI, CF, CIF, D, DI, DF, K, L, S, ST, T, LL1, LL2, LL3, LL01, LL02, LL03. Obtained on eBay.

Dietzgen Clear Scale

    Another very nice two-sided plastic rule. It lacks the LL01-03 scales of the Sterling, but it has two T scales (T1, T2). The green background on some scales is a nice touch. The cursor has multiple hairlines, many of which I can't figure out, but two of which are clearly a way to quickly convert from kiloWatts to horsepower. Bought on eBay.

Post Model 1460 Versalog

    It has a cracked window and needs some cleaning, but this big Sun Hemmi bamboo rule is otherwise pretty nice. The front has LL0, LL/0 (LL00 in more standard notation, the inverse line), K, DF, T, ST, S, C, D, R1 and R2, L. The back has LL/1, LL/2, LL/3, CF, CIF, CI, C, D, LL3, LL2, LL1. And, um, yeah, I think the stick was in backwards when I took the picture. Makes more sense to have CF and DF on the same side. Oddly, there's no A or B. R1 the square root of C, R2 extends that scale (so 9 on C gives 3 on R1 (square root of 9) and 9.49 on R2 (square root of 90)). Bought on eBay.

Circular Slide Rules

Scientific Instruments Co. Model 300-B
Circular Slide Rule

    This was the first circular rule I obtained, bought over the phone from Boston Museum, and it quickly got stolen off my desk at work. The inner wheels on both sides rotate independently and the radial cursor has the scales printed on it in red. Has the following scales: A, B, C, D, CI, K, L, LL2, LL3, S, T1, T2, ST. Made of laminated bamboo, came with a carrying case (which was also stolen, sigh).

C-Thru Proportional Scale Model PS-79
Circular Slide Rule

    Has only the A and B scales, plus a window which gives the percent size and multiple of reduction between the outer and inner wheels. Made from plastic sheets. I got this at the drafting section of the student bookstore at OSU, it's one of the few types of slide rule to hang on until the calculator age, although they too fade as layout is more and more handled on a computer.

Keyline Concise Rule

    A multi-layer plastic laminate with a turning inner disc and a cursor molded to fit over the raised central disc. Only has A, C, CI, D and K scales, and is very compact. The back has various conversion formulae between English and Metric. Stamped with Northrop Wilcox emblems, both on the rule and on its vinyl case. Comes with a small folded up page of instructions. Acquired on eBay.

Dietzgen Midget Slide Rule

    A single, immovable and rigid celluloid-coated aluminum disc with two cursors on one side and one cursor on the other. Most of the scales are unlabeled on the front, and I have no idea what the V versus U.S.S. scale is, or what the scale with letters rather than numbers is for (it does not seem to be a scale for setting the two cursors). The reverse side has multiple sine and tangent scales, plus conversion from fractions to decimal. The case is imprinted "A&B Smith Co." but that's no guarantee that this is the company that made the rule. While there are copyright dates (1936 for the front, 1931 for the back) there's no name of manufacturer. I have since found an eBay auction for another of these that claims it to be a Dietzgen Midget Slide Rule, and I got the seller to send me photocopies of the instructions so I know that V and U.S.S. are screw threading/tapping size systems.

Aero Products Research CR-4 Computer

    Built for pilots as a tool to figure out things they needed to know. Very few "standard" functions, mostly specialized stuff I don't really understand even after reading the included manual. Purchased on eBay.

    Stefan Vorkoetter points out that the scale just inside the B scale converts hours on B into minutes on the inner scale. Other front scales convert indicated and true airspeed (correcting for altitude, as airspeed indicators are sensitive to pressure differences). On the back are windspeed compensation calculators (as Stefan writes about here), and scales for finding vector components (TAS arrow on x, look next to the degree mark d to get x sin(d) or x cos(d) depending on whether you're looking at the black on white or white on black marks).

AN5837-1 Altitude Correction Calculator

    Another aviation rule, I got this one from American Science & Surplus. It's made by Cruver Manufacturing Co., and is a spiral rule that lets you figure out true altitude from indicated altitude by compensating for temperature. The only instructions are printed on the back, and I never quite managed to make it work in a sensible manner. But I don't really have avionics training.

Unusual Rules

K&E Desk Rule N-4096

    This rule is 22" long, and comes in a wooden box with latches to hold it in. Once removed from the box, it has metal legs it stands on. Designed for everyday simple jobs, it only has the C, CI, CF, D and DF scales. But with a single decade spanning 20", it gives pretty good precision. Being made of wood, however, it has warped slightly with age, so the precision isn't what it used to be. It comes with an instruction pamphlet extolling the virtues of the slide rule for use in the average merchant's shop. Part of the Walker Collection.

155mm Howitzer Slide Rule Set

    Purchased on eBay, this is a set of slide rules used by artillerists to aim their big guns. Based on the materials, I'm guessing it's Vietnam vintage or thereabouts. The small rule at the top is the only "slipstick" style, and seems to be a rough approximation rule, with the cursor sticks below it used for specific loads and uses. It seems like I'd need specially made charts in order to get any use out of these rules, though.

Slide Rule Tie Clasp

    I got this clasp on eBay missing the clip part (although I've since seen this model complete on eBay). I bought a cheap tie clasp and kitbashed the pieces together to create the thing seen above. It only has A, C and D scales, plus a cursor, and is 2" (5cm) long.

Nuclear Bomb Calculator

    Grant Pilkay sent me this book with included rule, meant to help calculate the effects of nuclear blasts. Sadly, some of the paint bound to the wrong side of one of the wheels and peeled off, so turning the wheel shows a gap. Click on the image to see at full size.

Picket N902-ES Classroom Demonstrator

    After years of trying, including some bot-sniped attempts on eBay, I finally got a demonstration rule for a price I could afford. It helped that "a price I could afford" went up recently. Pictured in my office, with the regular-sized N902-ES tucked onto the left-hand stand.

Metric Converters

Universal Circle Metric Converter

    Like the proportion wheel, this is another "hidden" slide rule. Sold by Chadwick-Miller (probably an office supply store), it uses two identical cylinder scales to do fixed multiplication tasks, converting units into metric and back to english. Rather than complicate things for the users, the log scales cover three decades explicitly, with things like .5 and 30 on it so users need not mess with order of magnitude estimates. Usually. Inches to feet requires dividing by ten. And the scales aren't lined up as well as they could be, this is just a cheap novelty item, really. The bottom scale is just a linear C/F temperature converter.

Sterling Pocket Metric Converter

    A simple metric converter like the pencil cup above. Made by a subsidary of the Borden company, it came in a plastic slipcase and had nothing on the back. In fact, the main body was molded out of fairly thin plastic, which had a broad T-shape cross-section. The back of the center piece has a temperature converter with a few notes like "Freezing" and "Fever."

Sterling 11" Metric Converter

    Same basic idea as the pocket converter, but about twice as long so that you can get more precision. It has a few more unit pairs than the pocket rule: length and area on the front, volume and weight on the back (no temperature). I got this loose (no paperwork or case) from someone who was doing some housecleaning prior to a move. :)

Sterling Engineers' Metric Converter

    A much more involved metric converter by the same company, it's twice as long as the basic metric converter and has tons and tons of units. Energy, flow, power, heat flow, velocity, density, pressure and so forth. Some of the units I don't even recognize, although the instruction booklet does explain them all.

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