Vernier calipers give measurements to a resolution of 0.001 inch, but people used to the easier-to-read displays of dial calipers might face a small learning curve the first time they measure with a vernier. Vernier calipers feature two separate scales: a main scale running along the centre of the tool and a smaller vernier scale that slides along the caliper parallel to the main scale. The relationship between the vernier scale and the main scale -- and the lines on their faces -- compose the elements needed to read a vernier caliper.
Identify the largest whole, long-lined marked number on the main scale that falls to the left of the "0" line on the sliding vernier scale. This is the starting whole number of your measurement, either in inches or centimetres.
Determine which line on the main scale aligns with or falls to the left of the "0" line on the vernier scale. The line may be a whole, marked number or a smaller line between whole numbers. The smaller lines represent either millimetres or 0.010 inch. Each 0.100-inch increment is marked by a smaller numbered line for ease of reading.
Compare the lines on the vernier scale to the ones on the main scale. Determine which line on the vernier scale aligns best with a line on the main scale. The value of that line typically represents 0.1mm or 0.001 inch; exceptions will be noted on the body of the caliper. The number of the best-aligned vernier line is the last part of your measurement.
Add the various parts of the measurement together. For example, if the last whole number to the left of the "0" line was 3, the "0" line fell just beyond the 0.120-inch line on the scale, and the "6" line on the vernier scale lined up best with the line opposite it on the main scale, the measurement will be 3.126 inches.