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While some posit about going back in time with a crate of AK-47s, I always muddle about what might happen if you go back in time with a crate of solar powered s

While some posit about going back in time with a crate of AK-47s, I always muddle about what might happen if you go back in time with a crate of solar powered scientific calculators. It may not have any impact whatsoever, but it's a curiosity of how much older engineering, finance, and/or economics may have been hampered by the speed, and precision, of calculation. It's also interesting to think about that scene in Apollo 13 where half of Mission Control are working Lovells/Hanks math (on slide rules) and muse about how we managed to get to the moon (and back) with likely just 4 to 6 significant figures. Slide rules are most definitely limited in that way.

deleted 4y ago
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derekp7 4y ago
From what I recall that scene was mostly adding/subtracting numbers -- which you can't do on a slide rule. So the slide rules were artistic license in the movie. This also leads into the fact that they did have plenty of computers that helped get to the moon, although slide rules were used for a lot of quick calculations and estimation by the engineers. And my favorite slide rule, the Pickett N-600, was carried on several moon missions as a backup calculation device. (Here's a picture of it on a Gemini mission: https://commons.wikimedia.org/wiki/File:Buzz_and_his_pipe.jpg https://commons.wikimedia.org/wiki/File:Buzz_and_his_pipe.jp...)
todd8 4y ago
Slide rules are good for only around 3 significant digits, just a little more than most people’s mental math for multiplication. However, slide rules include scales for squares, cubes, trig, exponential, log functions and others. All of these are inscribed as positions on logarithmic scales. In this manner, two scales can positioned to calculate products and quotients. The scales, being logarithmic, are very compressed on one end, between 9 and 10 is only 5% of the scale while the interval between 1 and 2 occupies 30% of the scale (log 2 == 0.30, log 9 == 0.95). If you can estimate measurements to a half millimeter on a precise ruler, on a one foot slide rule that corresponds to 508 divisions. Three significant digits requires 1000. With some careful interpolation while reading a slide rule it is sometimes possible to get 3 significant digits, especially in the range 1 to 2. It’s not possible to get 3 significant digits between 9 and 10. Another limitation of slide rules is that there are no provisions for addition or subtraction. For this there were mechanical adding machines. Notice too that all calculations are done with numbers in scientific notation. The scales start at 1 and end at 10. When calculating something like 447.8 * 1276, the slide rule is only able to calculate 4.48 * 1.28 for the user, and it gives a result like 5.73. The powers of ten have to be handled in one’s head. Furthermore, one has to understand trig well enough that having the sin only from 0 to 90 is good enough. Because slide rules don’t give very precise answers, tables of logarithms were used for calculations requiring 4,5, or 6 digits of significance.

deleted 4y ago

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derekp7 4y ago

From what I recall that scene was mostly adding/subtracting numbers -- which you can't do on a slide rule. So the slide rules were artistic license in the movie. This also leads into the fact that they did have plenty of computers that helped get to the moon, although slide rules were used for a lot of quick calculations and estimation by the engineers. And my favorite slide rule, the Pickett N-600, was carried on several moon missions as a backup calculation device. (Here's a picture of it on a Gemini mission: https://commons.wikimedia.org/wiki/File:Buzz_and_his_pipe.jpg https://commons.wikimedia.org/wiki/File:Buzz_and_his_pipe.jp...)

todd8 4y ago

Slide rules are good for only around 3 significant digits, just a little more than most people’s mental math for multiplication. However, slide rules include scales for squares, cubes, trig, exponential, log functions and others. All of these are inscribed as positions on logarithmic scales. In this manner, two scales can positioned to calculate products and quotients. The scales, being logarithmic, are very compressed on one end, between 9 and 10 is only 5% of the scale while the interval between 1 and 2 occupies 30% of the scale (log 2 == 0.30, log 9 == 0.95). If you can estimate measurements to a half millimeter on a precise ruler, on a one foot slide rule that corresponds to 508 divisions. Three significant digits requires 1000. With some careful interpolation while reading a slide rule it is sometimes possible to get 3 significant digits, especially in the range 1 to 2. It’s not possible to get 3 significant digits between 9 and 10. Another limitation of slide rules is that there are no provisions for addition or subtraction. For this there were mechanical adding machines. Notice too that all calculations are done with numbers in scientific notation. The scales start at 1 and end at 10. When calculating something like 447.8 * 1276, the slide rule is only able to calculate 4.48 * 1.28 for the user, and it gives a result like 5.73. The powers of ten have to be handled in one’s head. Furthermore, one has to understand trig well enough that having the sin only from 0 to 90 is good enough. Because slide rules don’t give very precise answers, tables of logarithms were used for calculations requiring 4,5, or 6 digits of significance.