Shown is a Post 1461 Pocket Versalog, 12.5 cm scale length, laminated bamboo core with celluloid overlay, engine divided (engraved) markings, metal framed glass cursor, metal end braces, adjustable. This size is known as a 5 inch slide rule. Made for Frederick Post Company of Chicago by Hemmi of Tokyo, Japan, from 1957 to 1972. This specimen was made in February, 1962. It is the pocket version of the Post Versalog 1460 10 inch rule. It is an open body duplex type slide rule with scales on both sides of the body and slide, and a single hairline on each side of the cursor.
K is for Cubes and Cube Roots
A and B are for Squares and Square Roots
CI is inverted C Scale, for Reciprocals, Chain Multiplication and Division
L is for logarithms. It reads the mantissa of the common logarithm.
C and D are the basic Multiplication and Division scales. Three Trigonometry scales S, ST, T are on the back of the slide.
Note: Some older slide rules do not have scale labels.
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The naming of slide rule scales was possibly the biggest design flaw in an otherwise wonderful work. It would have made far more sense to call the scales x, 1/x, x2, x3, etc., and some rules are made that way, particularly the French Graphoplex rules. For reasons lost to history, the scales ended up with meaningless letter names, especially A, B, C and D. It is likely that they first appeared to make it simpler to produce written instructions, as it can be very difficult to refer to the scales with no names at all, especially for a new user.
Some scales have no real reason to have the names they do; certainly K for cube is a stretch, but L for Log makes sense, as does S for Sine, and T for Tangent, and the added I for inverted or F for folded.
Many European and Japanese rules became self-documenting with the function added at the right end of the scale (x, 1/x, etc.), and the scale name letter appearing on the left end. This trend was not adopted in North America due to an attitude best summed up by the Pickett company, who felt that anyone smart enough to use a slide rule didnt need it. This user-hostile attitude was to carry over into the calculator and computer software disciplines to follow, a perpetual justification for poor user interface design. In Europe, the focus was to create the best possible tool, and their sophisticated but easy to use designs certainly reflect that attitude.
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Read the digits, then determine where your decimal point goes.
All the basic scales start and end with the digit 1.
Cursor reads 53 on C and D scales;
1887 on CI scale;
281 on A and B scales;
356 on BI;
149 on K scale;
0.848 on P;
32o on S;
27.9o on T
Note that the A and B scales are doubled. They have 2 cycles from 1 to 1. They are used for squares and square roots.
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The K scale is tripled. It has 3 cycles from 1 to 1. It is used for cubes and cube roots.
The slide rule shown is an Aristo 867 Darmstadt, 12.5 cm scale length, plastic, Germany. It is a closed body type of slide rule. Three log log scales are on the back of the slide.