Circle area calculation with a slide rule

Area calculation with a slide rule.

[michaelrafa]

I started using a slide rule back in the 1970s, before calculators were available. I never noticed the little c designation for computing the area of a circle of a given diameter!! Thank you!!

[martinfiedler]

Thanks. I knew how to make the calculation with the markers on the cursor, but the "C" was new to me.
That would be helpful with one of the models that do not have the shorter side markings 😃

Brings me to a follow-up questions: Some slide rules have a "C1" marking on the C scale; roughly at 3.57.
Do you know what this can be used for?

[Harjeet_Singh_M]

Helpful! Just the video I was looking for.

[jadenephrite]

Regarding 0:10, the C gauge mark is √(4/π) = 1.128 and is used to find the area of a circle on the A scale as calculated from its diameter on the D scale. For example, place the C gauge mark on the C scale over 2 on the D scale which is the diameter of a unit circle. Then go to the Left Index of 1 on the B scale and read above it on the A scale that the area of a unit circle is 𝜋 ≅ 3.14. The C1 gauge mark is similar to the C gauge mark. The C1 gauge mark is √(40/π) = 3.57 and is used to find the area of a circle on the A scale as calculated from its diameter on the D scale. For example, place the C1 gauge mark on the C scale over 2 on the D scale which is the diameter of a unit circle. Then go to the 10 at the middle of the B scale and read above it on the A scale that the area of a unit circle is 𝜋 ≅ 3.14. By comparison, the C1 gauge mark √(4/π) ≅ 3.57 is larger than the C gauge mark √(4/π) ≅ 1.128 by a factor of √10 = 3.16.

[tkarlmann]

Extremely poorly presented -- you put your text over the markings needed to be read!