# My Slide Rule Collection

## Lawrence Slide Rules

Festus Manufacturing Company made very inexpensive slide rules (painted wood, printed scales) for students. They changed their name to Lawrence and moved to Peru, Indiana.

Lawrence 10-B 10" Mannheim

This one has a magnifying cursor, which is kind of unusual for a cheap slide rule.

I have two of these. The case of one of them is integrated into the cover of a hardcover book, "The Slide Rule and How To Use It" by Hobart H. Sommers, Harry Drell, and T. W. Wallschlaeger. Grosset & Dunlap, 1942.

Lawrence 10" Mannheim

Lawrence Engineering Service changed their name to Engineering Instruments in 1947, so even though this slide rule has a different label than the one above, they're both from the same company. I have two of these. This slide rule was SO cheap that it didn't even come with instructions - the box was labeled "For instructions see page 95 Mathematics Made Simple Self-Teaching Encyclopedia"!

## Acu-Rule Slide Rules

Lawrence changed their name to Acu-Rule in 1940, and started producing slide rules under the name Acu-Math in 1950.

Acu-Rule No. 10-D, 10" Mannheim with Magnifying Cursor

This is also a very cheap slide rule; however, it has a magnifying cursor to make reading it easier.

Acu-Math No.1200, 5" Mannheim

I'm not sure if it's proper to call this a Mannheim slide rule or not: while the scales are right (K A[B CI C]D L, S T on back, actually a "polyphase" Mannheim because of the CI, K, and L scales), its simplex design isn't what I usually think of as a Mannheim.

At first I thought the extra hairlines on the cursor were for some mathematical use; they seem to be at 0.86 and 1.16 times on the C/D scales, and 0.74 and 1.35 on the A/B scales. I finally decided they were there because the end brackets on the stator prevent the cursor from being moved far enough to bring the center hairline to bear on the ends of the scale.

## Sterling Slide Rules

Sterling Plastics, the company that gave us the Rolodex, bought Acu-Rule in 1968, and was soon bought themselves by Borden, the milk company. Go figure.

The very last time I ever saw a slide rule for sale as a calculating instrument and not as an antique, was in 1985, and it was a Sterling. I bought it, and still use it in my workshop. It's a good rule to "put in harm's way", since it's easily replaced.

Sterling 584, 10" Mannheim

The Sterling 584 may well be the most common slide rule on eBay, usually labeled "WOW! RARE MINT ANTIQUE VINTAGE SLIDING RULER L@@K!!", no cursor, warped all to hell, an opening bid of \$99.99, and a reserve.

The top slide rule has only two bridges across the back, while all the other Sterlings have five. From Mike Konshak's Site I see this means it is an early version. How early? I don't know exactly, but the instructions do not list a zip code in the company address, implying that it was pre-1963.

The bottom two slide rules are 584 variants; the middle slide rule has red text on the slide, and the bottom slide rule has a green slide. There are other variants that I plan to collect.

Sterling 587, 6" Mannheim

Identical to the larger Sterling 584, only pocket sized.

Sterling "Decimal Trig Log Log", 10" Duplex

Not a bad slide rule for a Sterling. It seems to be the replacement for the very similar model 594 "Decimal Trig Multi-Log" - all the same scales, but no longer bears a model number and uses sans serif fonts. See Mike Konshak's Site of a 594.

I suspect that this slide rule not only replaced the 594, but also the Acu-Math version. I can't see any other reason to discontinue one model and produce a new model that is virtually identical. If this is true, this slide rule dates to after 1968.