Readings from which scale(s) are combined to form the measurement in analog micrometers?

• A. Only sleeve scale
• B. Only vernier scale
• C. Sleeve scale and vernier scale
• D. Sleeve scale, vernier scale, and thimble scale

Answer: (D)

The measurement from an analog micrometer comes from combining readings across three scales to get both the whole value and the fine fractions. The sleeve scale provides the primary length in millimeters, giving the main, fixed part of the measurement. The vernier scale adds interpolation between those fixed marks, yielding an extra digit of precision by showing which vernier line aligns best with the main scale. The thimble scale on the rotating spindle then supplies the final, smallest fractional portion of a millimeter as its lines align with the sleeve.

Read together, you add the sleeve reading (the integers), the vernier reading (the intermediate fraction), and the thimble reading (the finest fraction) to obtain the total measurement. This multi-scale approach is what lets a micrometer achieve high precision. If you relied on only one scale, you’d lose either the larger-scale information or the fine fractions, but using all three scales gives a complete and precise result.