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Slide Rules & the Electronic Engineer

Retronics series

Engineers translate ideas into products. They’re limited by the tools available for facilitating that translation. Over the span of my engineering career, those tools have undergone a dramatic transformation. I hope you will agree that it’s interesting to review on this month’s Retronics pages some of the rich history of those changes. First-hand knowledge of much of this material is fast disappearing. Fortunately, the web has some remarkable archives that will help to preserve it.

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Extra info / Update

January 27, 2011.

Correction

An incorrect page scan is reproduced in Figure 1. A scan of the correct page is available for free downloading here.

The beginning of the paragraph referring to Figure 1 should be modified and extended to read

Since common logarithms are exponents of base 10, you know that the “2” to the left of the decimal point means that the solution is larger than 100 but smaller than 1000. In Figure 1, none of the values matches the decimal fraction of your result exactly. The nearest value in the table is line 118, column 9, so you know that the antilog is a little less than 118.9. The selection of proportional parts mini-tables at the right makes it easier to interpolate between entries in the main table. The difference between successive values in the main table varies between 44 at the beginning and 30 at the end. The difference between row 118, columns 8 and 9 is 36, and your result of 07514 is 32/36 of the distance between them, or approximately 9/10. Thus, your final solution is Xc = 118.89 ohms.