Never thought about how a slide rule worked cause I always had a calculator, but inherited a slide rule from my dad and then found a pamphlet on slide rules when cleaning out my father-in-laws work shop.
So I added learning how to use a slide rule to my list of things to do when I had more than 8% of my weekly hours free to investigate interesting interests.
My slide rule has 6 scales, C, D, A, B, C1 and K. Scales B, C and C1 are located on the inner sliding section of the slide rule. I have not used C1 or K yet and may never. Slide rules also are supposed to have a third piece which provides a sliding section containing a hairline crossing perpendicular to all the scales. My slide rule was missing this and so I used a paper clip as a pointer. There are other variants of slide rules for different specific functions.
The scales have an index or starting point on both the Right Hand (RH) and Left Hand (LH) ends of the slide rule. If you can't find the answer, the other index is to be used.
Multiplication:
To Multiply 7 x 5, for example
- The C scale(bottom scale of the internal sliding section) right hand index is first set to 7 on the D Scale (bottom scale on the base of the slide rule)
- The hairline is set to 5 on the C scale.
- The result of 35 is read off the D scale at the hairline.
To divide 5 by 4,
- Set the hairline to 5 on the D scale
- Slide the C scale so 4 aligns with the hairline.
- read the result of 1.25 at the C scale Left Hand Index
Finding Cubes:
To find the Cube of 20
- Set the C scale Left Hand Index to 2 (20)
- Set the hairline to 2 (20) on the B scale
- Read 8 off the A scale
- Adjust the number on the A scale to get 800
Finding Square of:
Finding Square Root of:
- To square a number, look at the number on the D scale and the corresponding number on the A scale using the missing hairline device. The number 3 points to 9, the number 5 points halfway between 2 and 3 which is interpreted as 25.
- To get the square root is just the reverse.
