- Cursor to 4 on D
- Slide to 1.128 on C at cursor (1.128 is the gauge point c marked on the C scale on some slide rules, and is the square root of 4/π)

This uses the formula : Area = π d2/4. When dividing by the constant square root of 4/p in the example above, we are multiplying by square root of π/4. When we use the B scale for our answer, we are squaring this value and thus obtain the value π/4 and the square of the diameter, completing the formula.

Another method:

- Slide left index of C to 1.128 on D
- Cursor to 4 on D

Another method ... a direct use of the formula: Area = π r2

- Slide center index of B under π on A
- Cursor to radius 2 on C