The Principle of the Vernier Scale
A Vernier caliper operates on the principle of a Vernier scale, which is a secondary sliding scale designed to measure fractions of the smallest division on the main scale. This ingenious design allows for enhanced precision by leveraging the slight difference in spacing between divisions on the two scales.
Reading the Main Scale
To take a measurement, the jaws of the caliper are closed around or inside the object. The first step in reading a Vernier caliper is to observe the main scale. The value on the main scale immediately to the left of the zero mark on the Vernier scale provides the whole number and the first decimal place (e.g., in mm) of the measurement.
Reading the Vernier Scale for Precision
Next, one must identify which mark on the Vernier scale precisely aligns with any mark on the main scale. This aligned mark indicates the fractional part of the measurement. Each division on the Vernier scale represents the instrument's 'least count' or minimum measurable value, typically 0.02 mm or 0.05 mm.
Calculating the Final Measurement
The final reading is obtained by adding the main scale reading to the Vernier scale reading (the aligned Vernier mark multiplied by the least count). For example, if the main scale reads 12 mm and the 7th Vernier mark aligns, with a least count of 0.02 mm, the total measurement would be 12 + (7 * 0.02) = 12.14 mm.