Otis King
Interesting cylindrical slide rules, made from the early 1920s to the 1960s. These ones are very early - they have serial numbers in the A range, and also have the white-on-black scales that only occur in some early models - all the later ones are black-on-cream. Both of them are in very good condition, and both came wih their leather carrying pouch. But that is only the beginning... see if you can spot the differences between them:
The bottom calculator (Nr. A7303) is a relatively common (but early) Model L, with a black cursor. It has a 0-10 log scale on the bottom, with number 429, and scale 430 on the top, which consists of two parts, 1-10 log and 0-10 evenly divided.
The top calculator however (Nr. A8800), is rare as hens' teeth - not only has it hardly been used, it also has a nickeled cursor. That is not what makes it rare though. It is a different model, and not the model K that is also very common, but rather the model M, with scale nr. 441 on top (0.0025 to 100000 log - equivalent to scale nr. 418) and nr. 419 (1 to 10000 log) on the bottom. I have never seen another one like it.
There's an addendum to this story, from July 2019. We took a quick pre-brexit holiday to the UK, and went to visit some antique shops. One of the stalls in an antique center was a specialist barometer/scientifc instrument seller. He had various boxed Fuller calculators standing around from the 40 and 50s, for prices between £175 and £375, and also a cabinet with several Otis King slide rules, for prices between £60 and £120. The very cheapest one of these had black scales. I asked to look at it, and it turned out that, while it had no box or instructions, it did have the very early triagular shaped cap, a serial number with no letter prefix, no damage at all to the white-on-black scales, but, best of all, it had scales n° 422 and 424. Scale 424 is the monetary scale, making it a model N, not the far more common K or L. This combination of an early model N with black scales is rare as hens' teeth. If I would find this type of thing at a flea market for a ridiculously low price, I would offer a private seller a reasonable amount of money for it. But if you're a professional antiques dealer who prides himself in earning his keep with this stuff as your specialism, and you are happily prepared to overlook something that is stupidly rare, in that case it is not my role to show you any mercy. I have no idea why these weird and rare Otis King slide rules keep offering themselves up to me like this, while I don't even collect slide rules, but obviously, I snapped this one up, and I insisted on a 10% discount too. The nice lady keeping an eye on the antiques center suggested that I look at the others as well (bog standard later model K's and L's) which came with their box and instructions, and were "much nicer". And there probably lies the crux of the issue ...
See the pictures below of the model M n° A8800 and model N n° 5768 together.
A8800 model M (top) and 5678 model N (bottom). Notice the length of the slider is lnger on the model N.
Top caps - the triangular shaped cap on the right for n° 5768, the rounded cap with "made in England" for A8800.
The bottom of the slide rules, with serial numbers.
Scale 419 for the M, 422 for the N.
Scale 441 for the M, 424 for the N.
Identical patents.
Holborn viaduct address.
Since the length of the slider is different, so is the length of the bottom part of the calculator (and the bottom scale).
This is also visible with the calculators closed - the model N is still on the bottom.
For the right price, and to the right collector, both of these may be for sale ...