david_megginson, 1 month ago

Solving 2×2=4 is the #HelloWorld for any slide rule with the basic D and C scales, including the #CardboardComputer:

1. Adjust the wheels (or slide) to put 2 above 1
2. Keeping the alignment, read 4 over 2.

Not so hard, was it? There's a lot of unnecessary mystification around #slideRules, but they're simple tools at heart.

You can also try this with the online simulator at https://cardboard-computer.org

#DiY

Closeup of a homemade circular slide rule showing 4 on the outer D scale above 2 on the inner C scale.