**Last Updated: 1/16/21**

Pickett Model 3 added to long rules.

- Short Rules: Basically, pocket-sized straight rules.
- Long Rules: Still standard straight rules, but on the "too big for a shirt pocket" variety.
- Circular Rules: The original type of slide rule, a bit harder to find, but also used in enough specialty purposes that some still exist in actual use.
- Unusual Rules: My criteria are idiosyncratic, naturally, but any slide rule that I felt didn't fit into any other category goes here.
- Metric Converters: The big (sadly failed) push to get American on SI units happened in the slide rule era, so a lot of rules were made that are essentially just a bunch of A/B scales for unit conversion.

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. To give some idea how bad the old scans were by comparison, this was just sliderule1.GIF back in the day. Yes, GIF used to be used for something other than animation.

Another of Pickett's fine aluminum 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). Also has the "folded" CF and DF scales that start at π instead of 1, which is also seen on the business rule down in Unusual Rules, so I guess business sorts needed to be able to deal with round stuff? Comes in the same sort of nifty scabbard as the N600 above. This one has the first owner's name scratched into the scabbard, and the fact he was in Granvill [sic] Ohio.

The 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 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 to the age of my page, it had good search engine penetration at the time), 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.

This was my first Aristo rule, at the time I got it I hadn't heard of the
trademark (or the manufacturer Dennert & Pape) before. On the front side, it
has C, CF, CI, CIF, D, DF, K and L scales. On the back side are A, B, C,
LL0, LL1, LL2, LL3, S and T. It comes in a slim box that is capped at one
end. The cursor has to be all the way at one end for the rule to fit in the
box.

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.

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 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 front side has raised "bumpers"
at each end that connect the fixed parts together. When flipped over, the
bumpers keep the cursor raised off the table. 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. 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 several more hairlines on the cursor whose
purpose I haven't figured out yet. The left one on the A/B scale has a
separation that represents a multiple of about 1.28, the right side one on
the A/B scale has a separation that's a multiple of 1.34, and the one on the
C/D scale a multiple of 1.13. And there's one extra hairline on the CF/DF
scale on back, this a multiple of 1.145. Came in a leather scabbard with
Dr. Benenson's name stamped on the inside.

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.

A very cheap student rule made by Pickett, with A, B, C, D, CI, K, L, S and T scales. One-sided, kinda rattle-y. Traded one of several Microline 120s I got in the wake of the newspaper article for this. So, yes, this one is a bit out of chronological order, so is the yellow Microline 120 below.

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. 120s are
pretty common, I expect a lot of student bookstores stocked them. They're
mostly found loose, but I kept the one which had a decent case out of the
pile I started with.

I later acquired a yellow version of this, 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....

A 2001 eBay purchase, this is a fairly simple trig rule, but it came with all the packaging and paperwork, including the warranty card. The back of the rule 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, under Unusual Rules. Given the existence of the large demonstration rule version, I suspect that the N902 was another common college rule, a step or two above the Microline series and intended for those who were in majors that needed more than core math courses.

I don't remember where or when I got this rule, although odds are pretty good it was about the time I was moving to a new job, since I'd have been too busy to document stuff like this. The 903 is "Trig and Conversion" where the 902 is "Simplex Trig" and it has the "folded" scales on front. The back is similar to that of the 902, but it flips the top and bottom content, and the middle part has conversion tables.

This rule 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.

I didn't want to open the packaging back when I got this, but in the intervening years the blister crumbled enough to let me slide the rule out and look at it more carefully. This was the sort of thing that probably got sold in office supply stores and the stationery aisle of stores like Giant (Wikipedia has several defunct department stores by that name). There is no date on the package or the instructions, nor a copyright on the rule itself. It's slightly higher quality than the Microlines, if smaller. And I discovered upon removing it from the package that it has the S, L, and T scales on the back side of the slider...and unlike the Post 1444, you're supposed to pull it out and reverse it. The cross-section of the rule is somewhat hollow, to get maximum strength from minimum plastic.

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. I made it into an art installation as seen on the main page, and didn't feel like disassembling that to get a new picture of the back side, hence leaving up the ancient scan.

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, and seems to be Dietzgen's answer to the "ES" yellow scheme used by Pickett, meant for ease of reading.. 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 (1 hp = 1.055 kW). Some are probably the same π factors seen on the Aristo 970. Bought on eBay.

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, R_{1}
and R_{2}, L. The back has LL/1, LL/2, LL/3, CF, CIF, CI, C, D, LL3,
LL2, LL1. Oddly, there's no A or B. R_{1} is the square root of C,
R_{2} extends that scale (so 9 on C gives 3 on R_{1} (square
root of 9) and 9.49 on R_{2} (square root of 90)). Bought on eBay.

This one doesn't do many things considering its size, but it does them very precisely. In addition to having the LL and LL0 indices on back (although it refers to them as N1 or 1/N1 instead of LL1 and LL01) and the S, T, and ST on front, it also replaces the A and K indices with square root and cube root scales, taking a single decade and splitting it into 2 lines for square root, or 3 lines for cube root. This gives it the precision of a much longer rule for doing roots (for cube roots it's effectively nine times longer than using a K register to do cube roots at the same physical size). The back has a cheat sheet for using the different sliced up indices. It also has a few other indices I'm not familiar with, like DF/M or Co. DF/M folds at about 2.3 rather than pi, and looking that up I see it's the base ten log of e to three digits, useful in converting from natural to base ten logs. The Co index seems to be an unusual case of using a rule for subtraction, as the black oval number of the Co index is one (or ten) minus the number on the D index that it accompanies. Co for "complement"? It would have to be complementary angle in gradians, though (there's 100 gradians in a right angle).

Copyright 1947, made of a light non-ferromagnetic metal, but it doesn't look like aluminum unless it's really grimy...aluminum doesn't corrode the way this appears to be. Magnesium, perhaps?

(Expect an update on this soon, waiting on whether the person I got it from wants to be acknowledged.)

Circular Slide Rule

Circular 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 it also has the unusual "V versus U.S.S." scale and a scale with letters instead of numbers. I later got a photocopy of the instructions from someone selling another on eBay (these show up a lot), revealing that the V/U.S.S. scale was for screw threading/tapping systems, and the letters are the bit sizes. The instructions also revealed the manufacturer, something not actually printed on the rule itself. The reverse side has multiple sine and tangent scales, plus conversion from fractions to decimal. The case is imprinted "A&B Smith Co." The copyright dates are 1931 on the front and 1936 on the back, but the sheer number of these floating around makes it difficult to nail down the year of manufacture of any given sample.

(Original pictures from 2003)

(2019 pictures)

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).

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.

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 somewhat decayed instruction pamphlet extolling the virtues of the slide rule for use in the average merchant's shop. Part of the Walker Collection.

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 on the right 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, but if anyone can make sense of the instructions and can figure out how to use them alone, let me know. Click on either picture to show at larger size.

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.

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.

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.

A question from Chad Smith helped me figure out a neat trick not in the instructions that can be done with any metric converter with a cursor. Say you want to convert between two units of the same sort without a direct conversion, like miles to yards. Use the converter normally to convert the thing you have to something else, hopefully something that converts to the unit you want. Place the cursor on the answer, then very carefully slide the center stick to put that number as the input for another conversion. Continue until you get what you want. This is "indirect conversion."

Example: Using a rule with meters to yards and miles to kilometers, I want to find the yards in 3.50 miles. I place the center stick with the miles arrow on 3.50 and then line the cursor up with the number of kilometers. Kilometers to meters is just order of magnitude, so I'll multiply my final answer by 1000. Now I carefully move the stick so that the meters arrow is under the cursor, and read off 6.16 on yards (guessing on the last digit). That means 6160 yards, give or take ten yards...and 6160 is the correct answer.

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.

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."

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. :) Lots of yellowing (browning?) made obvious when I flip the center stick around. This has the same physical shape as the Empire Pedigree, so Empire probably licensed or stole the design from Sterling/Borden Chemical. (Or Empire was a subsidiary of Borden too.)

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 (mostly flow-related), although the instruction booklet does explain them all. As indicated by the case, this is part of the Walker Collection as well.

This is part of the class of "barely a slide rule" things that do still show up, especially for things like recipe unit conversion. Made in 1999, it's a temperature converter that includes the Rankine scale, which is the absolute temperature scale that is in Fahrenheit-sized degrees. While sold by Scientific Instruments, the back shows Datalizer Charts to be the maker. The back also proudly proclaims this to be ISO9001 certified.

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