How to Operate the Slide Rule

To Multiply Using a Slide Rule

• 1

  Slide the C scale to the right, so that it starts at one of the numbers you wish to multiply on the D scale. This lines up the 1 on the C scale with the number you wish to multiply on the D scale.

• 2

  Slide the cursor to the other number you wish to multiply on the C scale.

• 3

  Read the number on the D scale that the cursor is over. This is your result of multiplying those two numbers.

To Divide Using the Slide Rule

• 4

  Move the cursor to the number you wish to divide on the D scale.

• 5

  Slide the C scale so that the number you are going to divide by lines up with the cursor.

• 6

  Move the cursor to the closest 1 on the C scale. This may be to the right or the left.

• 7

  Read the number on the D scale that falls under the cursor. This is your result.

To Square a Number Using the Slide Rule

• 8

  Line all the scales up together.

• 9

  Move the cursor to the number you wish to square on the C scale.

• 10

  Read the number on the B scale that the cursor is over.

• 11

  Adjust the decimal points of the number on the B scale. This takes a bit of thought at times. For instance, if you are trying to square 4.7, the answer is approximately 22. But using the slide rule will read 2.2. We know that 4.7 squared must be larger than this so we move the decimal point to the right and get the result, 22.

To Find a Square Root Using the Slide Rule

• 12

  Decide which of the two B scales to use. The left half is used to find the square root of numbers with odd numbers of digits like 100. The right half is for numbers with an even number of digits, like 25.

• 13

  Change the number you wish to find the square root of into a decimal between one and ten. To do this you drop all zeros at the end of the number. One hundred would become 1. Also move the decimal point to change your number into a decimal. For instance 375 would become 3.75.

• 14

  Line all the scales up together.

• 15

  Move the cursor to the decimal on the correct half of the B scale.

• 16

  Read the number indicated by the cursor on the C scale. Adjust the decimal points of the number on the C scale as you would do in squaring a number. For instance if you are finding the square root of 4,500, you would turn it into 4.5. You would use the right half of the scale as 4,500 has an even number of digits. You would get the reading on the C scale of 6.7. The square root must be at least a double digit number, so we adjust the decimal point to get a result of 67.