A bin of slide rules

One of the finds from the 2022 Atlanta Hamfest that I’m most excited about is the bin of slide rules and slide rule books that Connie found at one of the flea market tables.

A bin of assorted slide rules and slide rule books
A bin of slide rules and slide rule books

There were 10 different slide rules and a total of 12 slide rules in the bin. Some of them were pretty basic slide rules, and some were more advanced with multiple scales, some of which I hadn’t seen before. These bring my slide rule collection up to 15.

I’ve made a first pass through the bin to check out the slide rules and jot down some notes about them. All of them are in pretty good condition, although one of them is missing the cursor. Two Keuffel & Esser rules, three Picketts, three Sterling, a couple very short pocket sized slide rules, and a little circular rule with some basic scales on it.

It will take me a while to research, photograph, and learn more about each slide rule. Should be a fun project.

My first slide rule

I grew up with electronic calculators and while I remember my uncle having a slide rule that I played with as a kid (didn’t know what it was at the time…it was just a neat looking thing with slide-y bits and numbers printed on it), I never used one until I got my first one in high school.

At the end of one of my high school math classes, I noticed the teacher using something that wasn’t a calculator to work out the grades on a test we just had. Intrigued, I went over and asked about it. He was using a slide rule, showed me some basic operations on it. He was calculating percentages faster on his slide rule than using a calculator. I thought it was just the neatest thing in the world. He reached into one of his desk drawers, pulled out a box, and handed it to me.

I had my first slide rule!

Ricoh No. 102 slide rule case
Ricoh No. 102 slide rule case
Ricoh No. 102 slide rule
Ricoh No. 102 slide rule

It’s a pretty simple beginner’s slide rule made of bamboo with a plastic reticle. It’s a single sided slide rule with a reversible slider. that has B/CI/C scales on one side and S/L/T scales on the other. Seems like this model would have been an inexpensive slide rule targeted at the student market.

The back side has some handy reference tables and formulas.

I taught myself how to use a slide rule and used it pretty regularly through my last year of high school and into my first couple years of undergrad. The main reason I stopped using it was that most of the problems became more symbolic, and the numeric problems I did get became complex enough that it was faster for me to use my calculator (HP-28S at the time). The slide rule stayed in the desk drawer for the rest of my undergrad and grad school.

Most of my calculations are done using spreadsheets now, but I pull the slide rule out every now and then for some quick calculations and to remind myself how to use it.

Slide rules

Acquired some slide rules this week (that makes three that I have now, so I think that qualifies as a collection). The new additions came from the estate of N6GA (SK) and were posted on one the amateur radio mailing lists I subscribe to. Both came in hard cases and are in pretty good condition.

Slide rules
Keuffel & Esser (K&E) 4080-3 log-log slide rule (top) and Pickett N-515-T Cleveland Institute of Electronics electronics slide rule (bottom)

The Keuffel & Esser 4080-3 slide rule has a serial number of 939707 (some nice symmetry in that number). Looks like this is a 1939 version, based on the scales on the rule and this catalog page.

The plastic brace parts of the reticle are broken, and there’s some corrosion on the metal frame. Think it might be possible to fashion some replacement braces out of bamboo or something similar. Looks like I might be able to purchase a used one too. No manual for this one, so I’ll have to see if I can hunt one down.

The other slide rule is a Pickett N-515-T. Seems like this particular model was made by Pickett for the Cleveland Institute of Electronics. Has some scales specifically for electronics related calculations and handy electronics formulas printed on the back. Not quite as chunky as the K&E slide rule, but it’s made of metal (aluminum I think) so it’s pretty rugged. No manual with this one either, but I was able to find some Cleveland Institute of Electronics slide rule course booklets online.

Will be fun learning how to use these slide rules.

Vintage mammography phantom

Just about every medical physicist has a collection of old test gear, phantoms, test objects ,meters and the like.

A few years ago, while rummaging through the equipment cabinet in our store room/library/lab, I came across a variant of a mammography phantom that I hadn’t seen before. Instead of the normal pink wax insert, this one had 16 wax squares of different colours.

Old RMI mammography phantom SN 152-1015
Old RMI mammography phantom SN 152-1015

Aside from the curved bit of plastic at one end of the phantom (a test object, not a ghostly apparition), it’s the same size as the conventional ACR accreditation phantom. Reminds me of one of those sliding number/picture puzzles where you have to slide the squares around to reconstruct the image.

Old RMI mammography phantom SN 152-1015
Old RMI mammography phantom SN 152-1015 side view

I let it sit on my book shelf along with some of the other pieces in the collection. A few months ago, I decided it was time to have a look and see what the inside of the wax blocks looked like.

Old RMI mammography phantom SN 152-1015
Old RMI mammography phantom SN 152-1015

Looks like at some point in its history, the pieces got a little scrambled and reinserted a bit randomly. I was expecting that each colour block would represent a different density. Instead there are the usual fiber, speck, and mass groups, but not nearly as uniformly placed as in the accreditation phantom.

I don’t know how old this phantom is or what time frame it might have been used at work. The only mammography phantom I was familiar with before this one was the pink one, so possibly before 1996 at least. Definitely pre-1999.

If anybody out there happens to know anything about this style of mammography phantom, let me know.

Museum: Collimator core

An essential component of any gamma camera is the collimator. Essentially a hunk of lead with a bunch of tiny little holes in it (modern collimators are made from ridged sheets of lead bonded together to form hexagonal holes like this one).
Collimator core
The purpose of the collimator is to restrict the direction from which gamma rays are detected by the gamma camera. They operate like blinders and make it so that the gamma camera can only see gamma rays coming from a particular direction (usually straight ahead perpendicular to the face of the camera). Collimators are necessary because by itself, the gamma camera has no idea what direction a detected gamma ray came from. By limiting the direction gamma rays are detected from, a useful image can be created by the computer.
This image I took by placing the collimator up against the front of my camera lens and a wide open aperature (f3.2). You can see just how limited the field of view becomes with the collimator.
Through the collimator

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