How should the diameter of the top be measured?

• A. in a circumscribing circle in 2 places
• B. by average of several vertical points
• C. in a circumscribing circle in 6 or more places
• D. by measuring one point with micrometer

Answer: (C)

When you measure a top that may not be perfectly circular, you want to capture its true usable diameter rather than a single local size. The correct approach is to envelope the object with a circumscribing circle and take measurements around the circumference in many directions. Using six or more measurement points around the circle helps average out any out‑of‑roundness or irregularities, giving a more accurate and representative diameter. A single micrometer reading or only a couple of measurements can be biased by local imperfections, while measuring across a circumscribed circle in many places ensures you account for the shape in full.