A hollow tube is measured with a vernier calipers. Corrected external diameter is D and corrected internal diameter is d. Which statements are correct?

Select all that apply

• Option A

  Wall thickness = (D - d)/2

• Option B

  Cross-sectional area of material = π(D² - d²)/4

• Option C

  If equal positive zero error affects both raw diameter readings and the same correction is applied, D - d is unchanged.

• Option D

  Wall thickness = D - d