Slide Rules

Engineers calculated with slide rules before electronic calculators became available in the 1970s. A slide rule has a body and a slide, both marked with scales, and a clear sliding cursor with a hairline. Slide rules may be straight or circular.

Even young students can learn the basics of how to use a slide rule with two very simple paper slide rules.

Paper slide rule for adding and subtracting

Print the template on paper or cardstock. Cut out the strips using scissors or a paper cutter. Make a cursor by drawing a thin line on small piece of clear plastic.

This paper slide rule is used for addition and subtraction. Both strips of this slide rule have an evenly spaced scale (linear scale), like a ruler with centimeters and millimeters. This is not like a real slide rule (real slide rules do not do addition and subtraction!), but it is a good way to start learning about slide rules.

Even young students who are learning addition can gain understanding from this simple slide rule.

Can you figure out how to do addition with this slide rule? Yes, you can. Just play with it and you will see. Can you understand why it works? Yes, you can. Just think about it.

Note: On a slide rule, a number like "3" may represent 3, or 30, or 300, or 0.3, so you must mentally keep track of the rough size of your numbers.

Using a paper slide rule to add 3+8=11 or subtract 11−8=3 or 11−3=8.

Using a paper slide rule to add 46+56=102 or subtract 102−56=46 or 102−46=56.

Paper slide rule for multiplying and dividing

Print the template on paper or cardstock. Cut out the strips using scissors or a paper cutter. Make a cursor by drawing a thin line on small piece of clear plastic.

This paper slide rule is used for multiplication and division. Both strips of this slide rule have an unevenly spaced scale (logarithmic scale). This is like a real slide rule (these scales are named C and D on a real slide rule).

Even young students who are learning multiplication may be enchanted by this alternative "magical" way to multiply.

Can you figure out how to do multiplication with this slide rule? Yes, you can. Just play with it and you will see. Can you understand why it works? Only if you know logarithms (you learn logarithms in high school). This slide rule multiplies numbers by adding their logarithms.

Note: On a slide rule, a number like "3" may represent 3 or 30 or 300 or 0.3, so you must mentally keep track of the rough size of your numbers.

Using a paper slide rule to multiply 2×3=6 or divide 6÷3=2 or 6÷2=3.

Using a paper slide rule to multiply 7×25=175 or divide 175÷7=25 or 175÷25=7.

Note: You can find other printable slide rules, both straight and circular, online.