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I was going to enter this into the "Party like it's 1929" contest because slide rules:
- Were used in 1929 (and earlier, but never at parties I'm afraid)
- Are an intrinsically easy to replicate technology; once you know how it works, you can trivially replicate it on any medium, such as soup cans, railway spikes, or discarded bills of hyperinflated currency.
- They work underwater, in a vacuum, in the sun, in the snow, in nuclear winter. Never runs out of batteries, and you can drop it off a building and it will still work. It is the ideal tool for the discerning scientist of the post-collapse-of-western-civilization world.
- Cannot be used to easily calculate compound interest far into the future, which no one should be depending on right now anyway, since real "wealth" gains are unpredictable in the face of uncertain inflation and prime interest rates in the short term.
Unfortunately I am both ineligible for prizes, and published this instructable way too long ago. Curses!
Slide rules are analog mechanical calculators. They were ubiquitous among engineers and scientists from their inception, to the development of cheap transistor calculators.
They allowed you to do quick calculations with an accuracy up to two or three significant figures. You can multiply, divide, perform exponential functions, square/cube roots, inverse functions, trigonometry, and others. You cannot add or subtract. (Actually you can but it's much harder than doing it in your head. Bonus points to whomever posts a method to do so as a comment.)
You do the math essentially by moving sticks around. If you learn how to use this, and actually do, expect to entertain questions from anyone under 40, and nostalgic comments from anyone 40 or over.
Now, all strangeness aside, I've found one situation where I really appreciated the slide rule: as a biologist doing field work.
In that special case, you know that nature is not so kind sometimes. You will freeze and burn, you will fall off things, you may be away from civilization for months. Storms can be pretty bad, and when they aren't, the countless insects scream for a blood meal. You will need to do math in absurd conditions.
So if you're part of that special group of people to whom this applies, this is a useful tool. In fact, you should never leave for the field without a slide rule and dice (for randomizing sampling and selection for treatment groups... "arbitrary" is just not good enough for proper statistics).
This photo is of the slide rule in its "start" position. The center plastic piece slides left and right, the plastic piece to the left (called the cursor) is also mobile. Most functions are accessed in this position... if you move the cursor so that it is centered on "2" on the bottommost scale, you will notice that it lines up with 8 on the X3 scale, and 4 on the X2 scale... which should come as no surprise.
But... it lands on 5 on the 1/X scale! This is our first lesson about slide rules. They do not indicate the decimal places. You need to remember that 1/2 is going to be less than 1, but more than 0.1... and thereby reason that the indicated 5 is actually 0.5. This sounds annoying but rapidly becomes trivial.
To perform the inverse of these functions, just look them up backwards. For instance, in this configuration, 6 on the X2 scale lines up nicely around 2.45 on the middle scale, which of course is the square root.
Next, we shall move to multiplication.
- Were used in 1929 (and earlier, but never at parties I'm afraid)
- Are an intrinsically easy to replicate technology; once you know how it works, you can trivially replicate it on any medium, such as soup cans, railway spikes, or discarded bills of hyperinflated currency.
- They work underwater, in a vacuum, in the sun, in the snow, in nuclear winter. Never runs out of batteries, and you can drop it off a building and it will still work. It is the ideal tool for the discerning scientist of the post-collapse-of-western-civilization world.
- Cannot be used to easily calculate compound interest far into the future, which no one should be depending on right now anyway, since real "wealth" gains are unpredictable in the face of uncertain inflation and prime interest rates in the short term.
Unfortunately I am both ineligible for prizes, and published this instructable way too long ago. Curses!
Slide rules are analog mechanical calculators. They were ubiquitous among engineers and scientists from their inception, to the development of cheap transistor calculators.
They allowed you to do quick calculations with an accuracy up to two or three significant figures. You can multiply, divide, perform exponential functions, square/cube roots, inverse functions, trigonometry, and others. You cannot add or subtract. (Actually you can but it's much harder than doing it in your head. Bonus points to whomever posts a method to do so as a comment.)
You do the math essentially by moving sticks around. If you learn how to use this, and actually do, expect to entertain questions from anyone under 40, and nostalgic comments from anyone 40 or over.
Now, all strangeness aside, I've found one situation where I really appreciated the slide rule: as a biologist doing field work.
In that special case, you know that nature is not so kind sometimes. You will freeze and burn, you will fall off things, you may be away from civilization for months. Storms can be pretty bad, and when they aren't, the countless insects scream for a blood meal. You will need to do math in absurd conditions.
So if you're part of that special group of people to whom this applies, this is a useful tool. In fact, you should never leave for the field without a slide rule and dice (for randomizing sampling and selection for treatment groups... "arbitrary" is just not good enough for proper statistics).
This photo is of the slide rule in its "start" position. The center plastic piece slides left and right, the plastic piece to the left (called the cursor) is also mobile. Most functions are accessed in this position... if you move the cursor so that it is centered on "2" on the bottommost scale, you will notice that it lines up with 8 on the X3 scale, and 4 on the X2 scale... which should come as no surprise.
But... it lands on 5 on the 1/X scale! This is our first lesson about slide rules. They do not indicate the decimal places. You need to remember that 1/2 is going to be less than 1, but more than 0.1... and thereby reason that the indicated 5 is actually 0.5. This sounds annoying but rapidly becomes trivial.
To perform the inverse of these functions, just look them up backwards. For instance, in this configuration, 6 on the X2 scale lines up nicely around 2.45 on the middle scale, which of course is the square root.
Next, we shall move to multiplication.
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The middle part of the slide rule is mobile. You move it around mainly when you want to perform multiplication/division. It works because one of the scales is linear, the other logarithmic.... and as I hope we all know:
log(ab)=log(a)+log(b)
log(a/b)=log(a)-log(b)
Note that in this photo, the slide has been moved so that "1" on the center scale is lined up with "2" on the bottom scale.
Now, note that "2" on the bottom scale is lined up with "4" on the middle, 3 with 6, etc. If you had lined up 2.15... you would then get 4.3, and 6.45 lined up.
Division just works by looking at this backwards.
But what if you wanted to perform 2 by 7? It goes off the end of the scale! Just slide the rule the other way.
log(ab)=log(a)+log(b)
log(a/b)=log(a)-log(b)
Note that in this photo, the slide has been moved so that "1" on the center scale is lined up with "2" on the bottom scale.
Now, note that "2" on the bottom scale is lined up with "4" on the middle, 3 with 6, etc. If you had lined up 2.15... you would then get 4.3, and 6.45 lined up.
Division just works by looking at this backwards.
But what if you wanted to perform 2 by 7? It goes off the end of the scale! Just slide the rule the other way.
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Apparently the Vedas were non writen text books (from a pre Gutenberg era) locked against errors by poetic rhyme and meter.
Some are mathematical methods, other seem to be 'James Bond science fiction soap opreas' that describe the detonation and effects of two neuclear bombs ('Gurka's Arrow' and 'The Iron Thunderbolt'), and all sorts of aircraft (Amaya) from baloons to rocket craft and even flying saucers.
Oddly enough, Robert Oppenheimer, who was the top scientist at Los Alamos during the Manhatan Project was an expert on the Vedas and recited one of Shiva's quotes after the Trinity test. ("I have become death, The destroyer of worlds.")
Did you ever find a circular slide rule (designed for electronics work) with 24 equally spaced marks on the face? Resistors, capacitors and inductors are seperated by the roots of 10. (20% components are seperated in value by the sixth root of 10, 10% components by the twelfth root of 10 and 5% components by the twenty-fourth root of 10.)
Scientific American ran this in a cool article a few years back "When Slide Rules Ruled" . I scanned then scaled up the page so it would be easier to "read between the lines". Fun and brings back memories of electronics class in High School. With the log function of a scientific calculator generate the numbers, mark them out with a (metric) rule and hey presto..! (Still stumped on how to make trig functions but I'm not a math whiz.) Did this once to make a log-scaled graph for capacitance/R computations- same principle applies for the rule, natch.