The arcane practice of nomography

Sounds like a third-century heresy

Roger Pollack has a blog of Cold-war calculators: “A collection of calculators created during the Cold War for the use of civil defense planners and military commanders.”

I suppose you could say that a nomograph is a graphical representation of a multi-variable formula. They can be difficult to make, especially for advanced applications, and there is really little pay-off to putting in the time to learn how. Like learning to sew well, it is a skill that cannot be expected to repay the cost of learning it.

I have always liked Nomograms. I learned a little about them in high-school drafting class, and a bit of the theory in college, but it was becoming archaic. Still, even today there are alignment charts of different kinds in use. I occasionally see (or use) one in a small engineering shop or at a company that makes specialized machinery. Someone forty years ago plotted out a nomograph to select the bearings for a particular application, and it is still in use, laminated and chained to a filing cabinet. Most have been replaced with spreadsheets, or suppliers’ proprietary computer programs.

They do have their advantages. A nomograph is relatively easy to use, and hard to misuse. It only works inside a defined range, and can only be used within that range. With a spreadsheet, any goof can change the formulas or copy another row to extrapolate outside of its legitimate range of use. With a (correctly made) nomograph, you can only use it for what it has been made to do. For example, if it is set up choose bearings to operate from 60 to 200 rpm, then the speed scale only runs from 60 to 200 rpm. It does not exist where it does not apply.

3 Replies to “The arcane practice of nomography”

  1. Oh, damn that is a cool collection. I may have one that is not in that collection: if so I will have to send the author some .jpg’s. I also have a USG book on the subject; fascinating reading, if ghoulish.

    I collect slide rules and one of my favorites is an East German artillery rule – about three pounds of solid aluminum and finely machined, and hilariously inaccurate.

    I have always thought a nomograph would have cut through the verbal and conceptual tangle that caused the fuel error of the Gimli Glider. The fuel crew had to calculate the fuel load manually, and (having just been trained in metric fueling units) got into an argument and mixed up a coefficient of expansion and a metric conversion unit.

  2. I have a few slide rules myself. I’ve seen pictures of a Soviet rule similar to the one you describe, also aluminum. That seems like a singularly poor choice of material, because of thermal expansion. I guess they were going for robust rather than accurate.

  3. Here’s the East German artillery rule. I don’t think aluminum is a bad material choice, as both pieces would expand/contract equally so it shouldn’t affect accuracy. But it would only need to be bent a little to become impossible to turn, so that would argue against aluminum and in favor of plastic.

    I recently acquired another Soviet rule – a copy of my favorite Japanese ‘Post’ rule that I use everyday – and I am planning to feature it soon in a side-by-side comparison.

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