What is a slide rule, and why was it’s invention such a big deal?
In: 1999
I haven’t seen anyone discussing converting numbers to powers of 10, which is an incredibly useful thing (add needed for using a slide rule).
If you wanted to multiply 12,567 by 200,768, you can convert these to 1.2567 x 10^4 and 2.00768 x 10^5. The power of 10 is how far you have to move the decimal point to make it an integer followed by the fractional part.
Now, you can get a fairly close approximation by multiplying the integers and adding the powers of 10 together: 1.25 times 2 is 2.50; adding the powers of 10 gives you 10^9.
So, 2.50 x 10^9 (or 2,500,000,000) is a pretty good approximation to 2,523,051,456.
On a slide rule, you would do your best to eyeball and line up 1.2567 on one scale and 2.00768 on the other scale, and probably come up with a number much closer than 2.50.
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