Unusual Slide Rules
I'm using this section for items from my collection that I think novel for one reason or another.
A couple of the slide rules in this section are genuinely rare, most are here because I've only come across them once in my years of local flea market crawls, which is a serious source of 'selection bias'. What I find are what the generations before me were using in the areas around where I live (or lived), with the exception of the first one on my list:
Finnish Radioactive Fallout Slide Rule
This is a very sturdy cardboard slide rule with instructions on the reverse.
The construction of the scales are similar to the BRL Radiac design. It is constructed from thick cardboard rather than plastic, and is labelled in Finnish. I find it gives a primitive and rugged vibe.
I own several Russian Slide rules, but slide rules labelled in Finnish don't seem too common.
Novotni Weight Slide rule
This slide rule looks quite spectacular, but is actually in quite poor condition. For a really pristine example, look here instead (Smithsonian).
The Novotni is a slide rule for blacksmiths. It calculates the weight of a material needed, given known material and dimensions.
The surface is black - supposedly it's Bakelite - and the markings appear to have been painted on the surface, as if stenciled or photo-transferred, rather than engraved. The scales could easily be worn off; much of the surface of my slide rule is missing scale markings.
Dietzgen Mannheim Slide Rule
I believe this slide rule probably dates to the late 1800s, though could be early 1900s. It is made of paperboard (cardboard) and has that famous old style metal cursor.
K+E 4138 Morrison Radio Engineering Rule
I found only three instances of the Morrison Radio rule having been sold on eBay in the last 20 years on Rod Lovett's eBay search engine.
This is an electronics slide rule specialized for radio communication engineering.
A manual with a good description of it's scales can be found on Clark McCoy's K&E pages .
K+E Mystery Rule
This slide rule has K&E logo stamped on the front. It is also marked "Chemco Photoproducts Company Ltd, Glen Cove NY", and "Copyright 1950". I haven't been able to find a mention of it from the Web. Chemco seems to have made circular slide rules for darkroom calculations, but I am not sure if this is intended for the same purpose.
The front face has 5 scales. A on the top, B, C, P, L on the slide. All scales are logarithmic, and the A scale length is about 18 inches. All scales have the same length per decade.
The A and B scales start at 1 and end at 50; so 1 and 1/2 decades. Relative to the A and B scales:
The P scale is folded (starts at 6), and ends at 300.
The L scale is folded (starts at 14) and ends at 700
The C scale is folded (starts at 10) and ends at 100, i.e., folded at 10 relative to A and B.
The slide rule came housed in a black wooden box, with hook locks. A screw under the slide ensures it can only move to the right, not left. I have examined the slide well , and found this was by design rather than a loose screw binding the slide.
It is mounted on metal brackets that hold it at a viewing angle of about 30 degrees from horizontal for better viewing angle. These brackets can be locked in place inside the box, in fact the slide rule appears to be designed to operate while in the box.
Willson Compressor Horsepower Computer
This Williams Compressor Horsepower Computer was manufactured by Willsonn Computers, based in Little Hocking, Ohio. They apparently specialized in oil and gas pipeline engineering calculators.
This calculator came with a mimeographed instruction manual and an advertisement for other slide rules made by Willsonn, which included the Willsonn Volume and Velocity computer, the Willsonn Pipeline Computer and the Sonney Orifice Computer.
It's a beautiful looking device, the master for it was hand drawn and lettered, with typewritten instructions.
MW Kellogg Equilibrium-Flash Slide Rule
I haven't been able to find any mention of this slide chart on the internet, so decided to drop it in the 'unusual' bucket .
This is a very specialized calculator, which allows process engineers in the oil and gas industry perform equilibrium flash calculations. MW Kellogg is now KBR, and they have a history in developments related to that industry, among others. This tool may have been used only within the MW Kellogg company.
I found a few videos on Youtube discussing the Equilibrium Flash concept, which oblige a bit more background in the surrounding subject area (thermodynamics?) than I'll find time for soon.
I gather ' Equilibrium flash' relates to how liquids under pressure 'flashing' to gas or vapour form when the pressure is removed; it is a function of pressure, volume, temperature, and the materials in question. In other words, it's a hairy calculation, which is why one absolutely needs this slide chart.
A manual came with it it, which I will upload later.
Magnum Double-Log Long-Scale Calculator - Log-Log-Spiral-Rechenscheibe
This belongs on the unique page not because it's rare...it's still being manufactured. It is an example of a hand-made instrument designed by Oliver Steffens. You can purchase any of a small number of models from his eBay store. I'm pretty sure I'll be going back for more.
This beauty comes with an inner set of logarithmic scales wrapped in a spiral around the center (e^x, x and e^(x/10) ), and an outer set of circular scales (y, sin y tan y, sqrt(1-y^2). I believe the spiral arrangement is known as a 'serpentine', not a very common arrangement in modern slide rules, but dates right back to the earliest models.
It's every accurate, and the inner scales
I'd also like to point out that Oliver has found a novel way to construct his slide rules that solves a problem that I have always had with home-made circulars, which is that his design allows the cursors to hold together at a constant angle during computation without relying on cursor-to-cursor friction. I'll be calling that the "Steffens method" as I plan to use it a lot on future builds.
Anonymous home-made slide rule (early 20th Century?)
I found this years ago in an antique mall. As a person who uses programming languages to slide rule scales for a hobby, this is a very special piece for me, because it shows someone decades earlier following a similar path. Another picture of this starts the 'home-made' section elsewhere within this site.
This 23+ inch (59 cm) slide rule is made from paper covered cardboard (laminated to provide grooves and edges for the slide and cursor). The cursor frame is wood and the cursor seems to be celluoid. The cursor has 2 hairlines (I'm not certain what the extra hairline is used for). The maker drew every line and lettered every number by hand.
Using modern slide rule nomenclature, this instrument has 2-cycle A/B scales on the top edge, a 1-cycle C/D pair on the bottom edge, and an L (log scale) in the middle. The scale lengths are about 19.6 inches (50 cm). The instrument doesn't have labels on the scales.
The log scale has very tiny numbers visible on the photo below (e.g., just about the "4" digit on the D scale).
Gauge marks for PI are on the A, B, C , and D scales
The ends of the slide and rule are protected by brass corners. One detail, probably not clear in the photos , is that the brass protectors are held down with 16 very fine screws. I have to assume these were mass-produced items that could be mail ordered. The screw heads are about 2.3 mm across, a bit bigger than a modern pin-head.
I have no real idea how old this is. The patina suggests it probably dates as far back as the 1920s to 1940s. Considering the materials used existed in the 19th century, it could be somewhat older. The tiny screws might help date the item, but as far as I know, these could have been standard parts for common items like clocks from the beginning of the 19th century.
