David Crate's Quality Slide Rules

Where we discuss:

Interesting, and Rather Unusual,

but Somewhat Obscure,

Slide Rules

The Hemmi #256

These instructions are for a Hemmi slide rule designed for problems in Electrical Communications. As most slide rules have a common set of scales, one can generally get by without a manual, or with a manual from another model rule. However, this approach is of no use in the case of the Hemmi 256. Thus, I am propagating the contents of a fairly ancient manual on the subject which was most graciously supplied by Mr. Cyril Catt of Lambton North, Australia.

Transcription of section: Calculation of Resonant Frequency.

Resonant frequency of electric current with inductance L and capacitance C is expressed by: F = 1/(2*Pi*Sqrt(L*C)), where "Sqrt" denotes square root and "Pi" is the famous ratio of a circle's diameter to its circumference. This kind of calculation is done with the use of the L, C' and F scales. Symbolic law of decimal point placement: F=L+C' (this determines the exponent or power of 10 of the answer. The scales selected for L and C have accompanying numbers, in red, to determine the exponent. These numbers are summed and subsequently used to find exponent of frequency)Example: find the resonant frequency for a circuit if L = 7 microhenries, C = 50 picofarads.Method: Set the red line F of the scale to 7 microhenries on the L scales. Set indicator to 50 pF on the C' scale, under the hairline read 85 on the scale F. According to the symbolic law of decimal point placement, from F=0+1=1, answer is found as 8.5 mc/s.

"KERCS" Project

I am now able to report encouraging news for sufferers of KERCS (K+E Rotting Cursor Syndrome). KERCS is a non-infectious but devastating malady endemic to 30's era K+E that were supplied with cursor guides composed of cellulose nitrate, a plastic with poor aging properties. After a few decades, the guides crumble and the cursor fall apart, leaving behind a beautiful but useless, slide rule. Now, working in collaboration with a California firm, we have developed prototypes of replacements for these pieces, made of modern, high-tech materials with better aging properties and close color and opacity matches. It is expected that these "K+E replacement cursor guides" will soon be available to the general public for a modest consideration. We will endeavor to keep you informed in the column. It would be appreciated if potentially interested parties would let us know of any interest at an early time.

KERCS Update (6-6-06)

They have finally arrived. Sets are available for $75. This includes both guides, eight tiny screws, and all shipping and related costs (they're small!). The material we selected is not as close a match as expected to the original color; it looked darker before it was cut into pieces! However, the parts are beautiful: one is etched with "KEUFFEL + ESSER CO. N.Y.", and the other with "PATENT 2,0862502". These parts are extremely faithful reproductions and will serve your slide rule well (even better than the originals). Please be aware that the supply is limited.

The plastic parts are milled on a numerically-controlled machine tool, drilled and tapped for the screws and then laser-etched with the lettering. The spring is then riveted on. Each piece is hand-finished.

Below is a photo of the prototypes:

And here is a photo of the production version:

A New KERCS Development: Reproduction K+E Indicator Frames (5-25-00)

We are being assisted in our effort to provide accurate reproductions of K+E indicator pieces by the former plant manager of the K+E plant in Connecticut. He presided over the shutting down of the K+E Slide Rule manufacturing operation there. He is redeeming himself now, however, by guiding us in the recreation of the indictor frames. We will be turning out a prototype in the next few months.

K+E Indicator Frames Update (9-2-02)

This project has undergone an indefinite delay as my partner's wife is ill and he has not been possessed of sufficient motivation to complete the prototypes.

Mathematical Digressions: the ubiquitous number "e".

Part one: a tally of "e"-sightings. (Please feel compelled to make a contribution. I am particularly interested in original ideas, so please send me an "e"-mail with your "e"-notion and I will post it with an attribution.)
1. Euler's famous equation for sinusoidal functions
2. The kernel of Gaussian functions (which are, in turn, components of all eigenfunctions of Fourier Transforms).
e. "e" raised to a power is an (the only) eigenfunction of the derivative operator.
3. e is even implicated in the ratio of prime to non-prime numbers. (Hadamard - the ratio of non-prime to prime numbers approaches a finction of 'e', as the numbers involved go to infinitity.)

4. ... ?

- Editorial Section -

Slide Rule Babe says: I cannot resist a man with a slide rule, Grrrrr!

So, Why Collect Slide Rules? (Other than to attract brainy women)

A reasonable question! It seems that slide rules represent, for me, the optimal collector's item in that they are found at the intersection of three rather synergistic realms: 1. Aesthetics: many of them are works of technical art - wood, engraved and paint-filled celluloid, metal and glass - they possess the beauty of fine tools. 2. Mathematics - they teach a lot about math if one troubles to learn to use it - and on a wonderfully physical level. 3. Rarity - slide rules are at the wonderful time in their history when no one makes them (as far as I know) but there are still a fair number around and the people that remember using them are still around, too. It's fun! And I find that the people that appreciate them tend to be of a rather nice sort.