slide rule magic


Today we celebrate the birth of someone whose dream has died in the blight of engineering black boxesWilliam Oughtred, inventor of slide rule.

At the outset of my career, I specialized in building computer models.  Big financial models.  The mortgage insurance industry, the postal system, telecoms accounting rates.  What became rampantly true was how much guess was piled on top of guess.  The output was engineered to resemble reality as seductively as possible, but its practical accuracy was opaque at best and random at worst. As computer models and black boxes proliferate, broader swathes of people forget the calculations and subtle dynamics behind these modelled phenomena.

Henry Petroski describes the intensifying hazards…

  • “The trend is clearly that eventually no engineer will own or use a traditional slide rule, but that practicing engineers of all generations will use – and misuse – computers…The vast majority of faculty [teaching engineering] did not ask where all those digits the calculators could display were going to come from or go to; they did not ask if the students were going to appreciate the approximate nature of engineering answers, and they did not ask whether students would lose their feel for the decimal point if the calculator handled it all the time…[In the times of the slide rule], excessively complex structures were eschewed by designers because the original sizing of members might be too difficult to even guess at, and calculations required to assure the safety of the structure were simply not reasonable to perform.  Hence engineers generally stuck with designing structures that they understood well enough from the very start of the design process.  What is commonly overlooked in using the computer is the fact that the central goal of design is still to obviate failure, and thus it is critical to identify how a structure may fail.  The computer cannot do this by itself.”

At the most fundamental, it all starts with the very calculations themselves. Some people muse whether learning long division is even a worth teaching in schools any more. Calculators pervade our electronically appendaged life with a lightning quick number crunching literally at our fingertips. But, like learning a foreign language that we will rarely use, or a physical prowess that we will never use to save ourselves in the wilderness, humans need these deep-dive skills to maintain an appreciation of the true essence of the world around us.