Don't know what a slide rule is for

-- Sam Cooke, 1960

I just can't remember any time in the past year when the act of writing and publishing single blog post has so lifted my spirits as it did yesterday.

Because I try to separate my logical from my emotional side, I need to examine why I found it so emotionally rewarding to write about something I always found emotionally unrewarding in the extreme. (Perhaps there's an inherent emotional reward in attacking the emotionally unrewarding.)

There's something very gratifying about letting go of the past. This, um, thing -- the so despicable slide rule -- a seemingly irrelevant detail from my life, mired as it was in forgotten detritus of American culture, has plagued me for most of my life, as my inability (failure?) to learn how to use it was one of those pivotal events which steered me into law school.

For me, the slide rule is literal and symbolic.

It is human morality, on a sliding scale. The slide rule is proof that there is such a thing as cultural and moral relativism.

Slide rule morality?

Not quite as insane as it looks.

First, consider it as a cultural artifact:

Throughout the 1950s and 1960s the slide rule was the symbol of the engineer's profession (in the same way that the stethoscope symbolized the medical profession). As an anecdote it can be mentioned that German rocket scientist Wernher von Braun brought two 1930s vintage Nestler slide rules with him when he moved to the U.S. after World War II to work on the American space program. Throughout his life he never used any other pocket calculating devices; slide rules obviously served him perfectly well for making quick estimates of rocket design parameters and other figures. Pickett brand slide rules were the standard in the Apollo program; Pickett's slide rules of the era often included a NASA or Apollo logo to promote the fact. A Pickett N600-MES (6 inch, magnifying cursor, "Eye-Saver" yellow) was standard equipment on all Apollo flights.

Some engineering students and engineers carried ten-inch slide rules in belt holsters, and even into the late 1960s this was a common sight on some campuses. Students also might keep a ten-or twenty-inch rule for precision work at home or the office while carrying a five-inch pocket slide rule around with them.

The slide rule required reason and understanding, and learning to use it well took ordinary mathematics into another plain. In effect, learning to use a slide rule required relearning math, or at least learning to think about it in another, new way. It was thus a cultural stepping stone, a true rite of passage. It is not exaggeration to say that it separated the men from the boys.

Much as I hate it, I must recognize that the slide rule had an elegance all its own, something that has been largely forgotten along with its demise. Common sense was built into the slide rule. Without the former, the latter was impossible to use. Even today, this is something button pushers forget at their peril:

A slide rule tends to moderate the fallacy of "false precision" and significance. The typical precision available to a user of a slide rule is about three places of accuracy. This is in good correspondence with most data available for input to engineering formulas (such as the strength of materials, accurate to two or three places of precision, with a great amount—typically 1.5 or greater—of safety factor as an additional multiplier for error, variations in construction skill, and variability of materials). There's an old saying in engineering, "if you care about the third significant digit of tensile strength, you are already in trouble." When a modern pocket calculator is used, the precision may be displayed to seven to ten places of accuracy while in reality, the results can never be of greater precision than the input data available.

Nonetheless, the cultural icon remained on display in certain circles:

Computers also changed the nature of calculation. With slide rules, there was a great emphasis on working the algebra to get expressions into the most computable form. Small terms were approximated or dropped. Fortran allowed complicated formulas simply to be typed in from textbooks. Numerical integration was often easier than trying to find closed form solutions. More difficult problems could be solved. The young engineer asking for computer time to solve a problem that could have been done by a few swipes on the slide rule became a humorous cliché. Many computer centers had a framed slide rule hung on a wall with the note "In case of emergency, break glass."

Notwithstanding its obvious virtues, there really is no rational argument which can be made for bringing the slide rule back.

Culture was changed.

Was morality changed too? Or is there no such thing as morality in numbers? (Oddly enough, the calculator represents the triumph of absolutism over the slide rule's inherent relativity, but that's a supremely relative irony that I'm afraid only Steven Malcolm Anderson would appreciate, God bless him....)

Emotionally, I think it's a good thing for me to let the slide rule go.

UPDATE: As Glenn Reynolds notes, people continue to grumble about the ways in which digital technology has changed the nature of human thought:

We need to listen to the expert warnings about the potential impact of digital communication on how people think and learn

(If we have to move in reverse, I'd prefer the abacus!)