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Slide Rule(s)!

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There is an interesting post by Mark Chu-Carrol about these wonderful calculating devices called slide rules. These are simple devices before the pre-digital calculator age and was the hallmark of every nerd worth his salt. That reminded me of my own experiments with these amazing devices.

I was born into the age of digital calculators and computers and hadn’t heard of the word “slide-rule” before my ninth standard. I came across that only when studying the history of computing devices. And only then I realised that I had been using primitive slide rules for quite sometime during my early school years to cheat in exams. That too, as early as the second standard. Here is what I remember of how I discovered these devices and my experiences with them.

In India, one of the first things you learn in your second standard is this concept called the number line. Though the only numbers we talked about were natural numbers, there was a lot of importance to the number line itself. Infact, undue importance was given to the number line and you were basically scrutinised for not drawing neatly rather than whether you got it or not. The teacher took painstaking effort to make sure every student had a neat and legible number line and drawing it was a mere ritual in itself completely devoid of any purpose or meaning.

During one of these drawing bouts, I noticed that these number lines could actually be used to do mindless addition. Mindless addition is pretty much what you do when you use a calculator and not the boring “3 in the mind, 4 in the hand” nonsense. Infact I had got so interested with discovering that I could do quick addition using a number line that I first used a single number line and marked ruler, which was primarily used for drawing the number line. Infact most of my teachers would think I was painfully measuring to draw the number line while I was actually having fun doing lots of addition. Then I had evolved into using two identical rulers to do addition. Somtimes, during normal exams, when two rulers could arouse suspicion, I usually took a 30cm ruler and broke it into two rulers of almost equal length. It was a matter of time before I got used to looking at the number lines in reverse, that I could even do subtraction.

Infact I had tuned my basic arithmetic so much to this primitive slide rule that I always used two marked rulers (used by everyone else for drawing the number lines) and was calculating things in a jiffy. Since I was pretty much diffident through out my school life, very few people actually knew of this trick.

The Math Olympiad.

Around this time was when my eye-sight was getting bad. I couldn’t read what was on the black board and hence couldn’t be very attentive in class. In concordance with that, my grades in all subjects (except math) had been uniformly falling. My shy nature wasn’t helping either and I was usually regarded as a “not-so-interested-in-education” types in school. And that label, usually meant you lost all respect in the eyes of your classmates. Though I wasn’t particularly bothered with the lack of “social” respect or my falling grades, I was very much interested in things like science and math. By that time I had usually taken to reading encyclopedias and knew a lot about astronomy and basic science by then.

So it happened that there was a sub-junior level mathematics olympiad and it was given to everyone in class, and I had come prepared for this. With two 30cm marked rulers of course. All questions were about adding and subtracting 4 digit numbers and some basic geometry. Infact the toughest question consisted of figuring out the missing numbers in an addition problem (i.e, subtraction – gasp!). I had gotten so good in using my slide rule to do addition and subtraction that I had finished the paper before anyone in my class did. Even before the official “bright” kids.

And surprise, surprise – I had won both by score and by time. Sometimes, its just amazing what a slight edge in technology could do.

Signing Off,
Vishnu Vyas.


Written by vishnuvyas

September 17, 2006 at 2:55 am

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