# Understanding the basics of the slide rule

ASSOCIATED with slide rules, we occasionally see quite unfamiliar scales which have been evolved for special purposes by people who have many calculations of a peculiar nature to make. If a complete collection of such special scales could be made, it would, no doubt, furnish an interesting study, and occasion surprise on account of its diversity. Log-log scales are less frequently used than the scales we have so far studied, but they are not in any sense "special" scales. The sliding center bar is sandwiched by the outer bars which are fixed with respect to each other. The metal "window" is inserted over the slide rule to act as a place holder. A cursor is fixed in the center of the "window" to allow for accurate readings.

The scales A-D are labeled on the left-hand side of the slide rule. The number of scales on a slide rule vary depending on the number of mathematical functions the slide rule can perform. Multiplication and division are performed using the C and D scales. Square and square root are performed with the A and B scales.

The numbers are marked according to a logarithmic scale. Therefore, the first number on the slide rule scale also called the index is 1 because the log of zero is one. Example - To multiply 3 by 2: Move the sliding middle section with scale "C" so that the 1 on the scale matches the 3 on the lower fixed section with scale "D".

Now read along the top scale to the 2 and see what it says on the bottom scale. The bottom scale should read approximately 6 which is the answer. We have just added a log of 3 distance on the bottom to a log of 2 distance on the top to get a log of 6 distance on the bottom.

Calculating 3 x 2 on a Slide Rule The slide rule also works for numbers larger than what is represented on the scale of the ruler. For example, double digit numbers can be represented by mentally "moving" the decimal places. Calculating 30 x 20 on a Slide Rule To perform division, simply reverse the steps for multiplication: Set the divisor on the C scale opposite the dividend on the D scale Read the result of the D scale under the C scale index where the scale reads 1 To multiply multiple numbers: Perform the multiplication method for the first two factors as previous described.

Then move the C index to the previous product to start the next multiplication. The hairline or cursor was handy for keeping a pointer on the previous product while moving the slide. To find the square root of a number: The A and B scales are the squares of the D and C scales, respectively.

To determine the square root of 9, look on the A scale for 9. Find the answer, 3, on the D scale below the A scale. To find the square: Reverse the square root process to find the square. There may be confusion about which side of the A scale to use.

## How to Use a Slide Rule (with Pictures) - wikiHow

For example, the square root of 4 is 2 and the square root of is 20 - both calculations can be found using the left side of the A scale.Basic Slide Rule Instructions. To multiply two numbers on a typical slide rule, the user set the left index (start of the scale) on the C scale to .

The slide rule is mechanical device used by mostly engineers and scientists for fast and accurate multiplication, division, to find roots and powers, and other simple math problems.

It consists of a fixed section with upper and lower parts marked with different logarithmic scales, a center. Get this from a library! Understanding the slide rule.. [R F Graesser].

## Basic Multiplication

The slide rule made it easier to utilize the log relations by developing a number line on which the displacement of the numbers were proportional to their logs. The slide rule eased the addition of the two logarithmic displacements of the numbers, thus assisting with multiplication and division in calculations.

understanding the slide rule. johnson, ronald e.; and others.

## Understanding the slide rule. (Book, ) [regardbouddhiste.com]

a booklet designed for elementary school students to be used independently from and in addition to the regular classroom curriculum in mathematics is given. the fifth- or sixth-grade student is presented with a discussion of the applications of the slide rule and with a background. Knowing this, the calculation becomes a simple division.

This technique can also be used on rules without an ST scale. Example: calculate sin(°) Move the cursor to 3 on the D scale. Slide on the C scale to the cursor. Most rules have a .

How A Slide Rule Works