POST Versalog Studies, Handbook for Electronics

Published 2025-10-29

By Christopher Howard

Recently I returned from a two week trip to New York, which was a combination family vacation and a trip to visit some of Emily's friends. There were many things on the schedule, but nevertheless I had a few hours each day to spare, where for various reasons I couldn't leave the house, or we weren't going anywhere. I took advantage of the opportunity to work through the POST Versalog Slide Rule Instructions, which from what I can gather was the standard slide rule text of the day. I worked through basically all the problems in the instructional chapters, and also I worked through the electronics applications chapter.

I learned a lot about using the various scales, including the standard scales (C, D, CI, DI), the folded scales (CF, DF), the square root scales, the Log Log scales, and the trigonometry scales. At first, it was intimidating trying to remember the various ways you are supposed to use the standard and folded scales in various multiplication scenarios. However, as I practiced with it more, I realized that I don't need to memorize the exact steps. Rather, one starts by getting a basic idea of what the scales are (logarithmic, inverted, and folded). Then, one gets a feel for the basic ways of how the indexes and the cursor can be positioned for multiplication and division operations. For each calculation, you first perform a simple mental estimation, to give you a rough idea what answer would be plausible. E.g. if you have 2.3 x 5.9, you know your answer is going to be somewhere close to 2 x 6 = 12, or 1.2 on the scale. Then you just pick the scales that seem most convenient — e.g., the least amount of movement of the sliding ruler — and position the cursor and maybe index in a way that gives you a plausible answer.

Another neat thing about using the slide rule is that, once you grasp this positional feel of things, you can do some basic algebraic problems without having to rearrange your operations. E.g., if you are trying to solve 2.3 x M = 13.6, using the CI and D scales you could just set the cursor for 2.3 on the D scale, put the C index where you would expect it to end up — at 13.6 over the D scale — and the see what value you got at the cursor of the CI scale — i.e., what value you would have used if it was a standard multiplication operation.

The trigonometry scales are not difficult to use, as these marked values each map to a value on the C scale. One can get confused about where to put the decimal place, so the standard slide rule construction has these range of decimal values noted on the side of each trigonometric scale.

Working through the practice problems in the applications chapter made me realize how much I can learn in electronics (and other fields) by working through the math in the examples or practice problems. Enjoying myself so much, I also started to work through the example problems in the Handbook for Electronics Engineering Technicians, by Kaufman and Seidman (1976), which was a book that I had on hand. I made it through the chapters on resistance and capacitance, and worked through some of the examples in the chapter on coils.

For the trip, I brought only my half-width DECI-LON K+E slide rule, as the most convenient option to store and carry. Generally, I like this slide rule, and the scale arrangement is nice, but my chief complaints are that (1) the slide moves so freely that is very easy to accidentally bump it out of position, and (2) the cursor is held in place by a curved piece of metal — acting like a spring — which I think is not aligned perfectly, and also the hairline tilts if you try to move the cursor from the side that has the spring. And obviously the scale marks are closer together.

Earlier, I had indicated that it is usually necessary to keep track of the exponents separately, using scientific notation. That is sometimes wise, e.g., in problems involves large differences in orders of magnitude, like when working with volts and picofarads. But for a lot of calculations, just using your mental estimate might be sufficient. E.g. 29.4 / 310.2 is going to be close to 30 / 300 = 10/100 = 0.1. So you know your answer should be something near the range of 0.09 - 0.11.

So far, I have really enjoyed learning how to use the slide rule, and — in a way that is somewhat difficult to explain to others — it has made mathematics and engineering feel more tangible and more like an adventure — an exploratory expedition, if you will.

Copyright

CC BY-SA 4.0 Deed