Carbic Otis King K

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Carbic Limited, Otis King's Pocket Calculator, Model K

Unit Closed

Unit Extended

Type: Cylindrical
Size: 6.25-10.5 inches / 16-26 cm; Scale effective length 66 in / 168 cm
Material: Steel, varnished paper scales
Scales:
- [ Scale 423 ] Scale 414
HvH: 588

With box and eight-page folded instruction sheet. Two copies:

Serial number P2924, manufactured around 1950-1
Serial number B7500, manufactured around 1983-4

Is that a five-foot slide rule in your pocket, or are you just happy to see me? Well, yes. If you could carry around a 5-1/2 foot slide rule, with the added precision that implies, wouldn't you? Most of the time, your basic 10" sliderule does the trick. Sometimes, you need a little extra boost from your buddy's 20" model, especially if your answer was up at the high end of the rule where precision starts to suffer. And sometimes you need the big guns, but at a reasonable price.

Cylindrical slide rules weren't novel when Otis King patented his calculator. But they were expensive and hard to use. But for the finicky engineer on a budget, needing 4 significant figures wherever he went, the Otis King calculators couldn't be beat.

The rule comes in two parts, separated by a cursor. The handle held the stator, with Scale 414 which we'll set up as analogous to a D scale. The far end slid in and out and rotated freely within the handle; this held scale 423, a double-length scale with three indices. Think of this as a double-length C scale. If you always set your middle index against your multiplicand (that's that number there on the D scale), you'll never have to wonder whether you've got the right end. Every number on D would have a corresponding number on C.

And that's all there is to the Model K. Set the cursor against the multiplicand on the stator, move the slide so the middle index is also against the cursor, then move the cursor until you find your multiplier on the slide ("C"). Read your product on the stator ("D"). Bang! 4 significant figures, 5 if you squint a bit while you're interpolating.

Carbic Limited was the manufacturer, and you can see that on P2924's instruction sheet, right underneath the label the retailer stuck on there so you would remember where you got it. This might be cheesy, but the retailer in question is the famous Negretti and Zambra, makers of a plethora of navigational, weather and survey instruments in the 19th and early 20th centuries.

For people who track such things, the address given by P2924 for Carbic, under the label, is 17 Seymour Place, London W.1. The address on B7500's manual is for Whitton Precision LTD, Bridge Works, Durnsford Road, Wimbledon, SW19 8DR. (This address appears on the back page and may be the distributor's overprint. There is no address on the front.)

B7500 kind gift of Gayle Teller.