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How to use The Slide Rule



• Simple multiplication uses C and D scale

• “wrap around” multiplication uses C and D scales

• Folded-scale multiplication uses C, D, CF and DF scales

• Multiplication by π uses D and DF scales


Example: calculating 2.3 x 3.4


 - Slide the leftmost index 1 on C over 2.3 on the D scale

 - Move the cursor to 3.4 on the C scale

 - The cursor is on the D scale just a bit over 7.8 or 7.82. This is the answer.



• Simple division uses C and D scales

• Reciprocal uses C and CI scales


• Example: Calculate 4.5 / 7.8

 - Move the cursor to 4.5 on the D scale

 - Slide 7.8 on the C scale to the cursor

 - Move the cursor to either the leftmost or rightmost 1 on the C scale, whichever is in range. In this case,                                  you would move it to the rightmost 1

 - The cursor is now at 5.76 on the D scale

 - We know that the correct answer is near 4/8 = 0.5, so we adjust the decimal place to get 0.567.