Difficulty: Moderately Challenging
Step1
Line up a number on the C scale—2 for example—with the number it's being multiplied by on the D scale—say 4. Shift the slide to the right to do this.
Step2
Leave the slide rule where it is and find 4 on the C scale.
Step3
Look once more at the D scale. You'll see that 4 on the C scale corresponds with 8 on the D scale. The number on the D scale—8 in this case—is the answer to your multiplication question (2 times 4).
Step4
Reverse these Steps 1 through 3 for division. Line up the divisor (8) on the C scale with the dividend (4) on the D scale. Again leave the slide rule where it is and find 4 on the C scale. The corresponding number on the D scale gives you the answer: 8 divided by 4 equals 2.
Step5
Use the lower scale for bigger problems. When no numbers correspond on the slide rule, shift it to the left instead of to the right. Here you'll be multiplying by tenths rather than whole numbers so remember to move the decimal points to get the correct answer.
Step6
Use the smaller graduated lines for tenths of a number. Bigger slide rules had more lines enabling them to get surprisingly accurate.
