How to Read a Circular Slide Rule
Slide rules are mathematical instruments which can be manipulated to solve various types of calculations. The first slide rules were straight-edge implements, leading to the rule portion of the name, however the design has since been modified to create a circular rule, also known as a radial slide rule. Circular slide rules can be used for many different types of equations, however, it is best to familiarize yourself with the rule by learning to multiply and divide using the circular slide rule.
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Instructions
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Converting your Numbers to Fit the Rule
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1
Convert the values being calculated to numbers which appear on the dials of the slide rule. The numbers of the dial only reach a certain level, and if your numbers are above this, you will have to convert it to use the slide rule. Multiply or divide by a value of 10 to a power, meaning numbers like 10 or 100, which feature a 1 digit first, and a series of 0's after, with a multiplication shifting the decimal right one digit for each 0, and division left once for each zero.
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2
Perform the calculation as described in Section 2 or 3.
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3
Convert your result from Section 2 or 3 into your final value by accounting for changes made in Step 1. For a change to a number being multiplied, or to the number being divided, reverse your actions. If your number was divided by 10 in Step 1, Section 2 or 3 will yield a value 10 times smaller than the correct value, and your number must in turn be multiplied by 10. For a change made to a number which another number was divided by, perform the same alteration you did in Step 1. For example, if in Step 1 you had to multiply the number you divided by in Section 3 by 10, your answer is 1/10 its correct value, and the result of Section 3 must also be multiplied by 10. It is possible to have to account for both numbers in the calculation.
Multiplying
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4
Align one of the numbers being multiplied on the outer ring with the 1 value on the inner ring.
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5
Locate the other value being multiplied by on the inner ring.
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6
Read the value on the outer ring, and perform any alterations as described in Section 1 to find your value.
Division
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7
Rotate the outer ring of the slide rule so that the number being divided on the outer ring is aligned with the number you will be dividing by on the inner ring.
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8
Locate the 1 value on the inner ring.
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9
Read the outer ring number which is aligned with the 1 marker, and convert the number if needed as described in Section 1.
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