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Vernier calliper
Beginner
A sliding scale that reads to a fraction of the smallest main-scale division.
LC = 1 MSD − 1 VSDA vernier has a main scale and a sliding scale whose divisions are slightly shorter. The smallest reading, the least count, is the difference between one main division and one vernier division. The reading is the main-scale value just before the zero of the vernier plus (matching vernier line × least count).
Main scale in mm, 10 vernier divisions equal 9 main divisions, so LC = 1 − 0.9 = 0.1 mm. If the main reading is 23 mm and the 6th vernier line matches, the length is 23 + 0.6 = 23.6 mm.
Check for zero error with the jaws closed and subtract it from every reading.
In more detail
A vernier calliper has a main scale and a sliding vernier scale. The least count is the smallest main-scale division minus one vernier division, which gives readings finer than the main scale alone.
Real-world uses
- Machinists measure shaft and hole diameters to hundredths of a millimetre.
- Jewellers and pharmacists use callipers to check small components accurately.
- Engineers use vernier callipers to measure the outside and inside diameters of pipes, shafts and bolts to a fraction of a millimetre.
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Frequently asked questions
What does least count mean?
It is the smallest value an instrument can read reliably. For a calliper it is found from the main and vernier scale divisions.
How do I read a vernier scale?
Note the main-scale reading just before the zero of the vernier, then add the vernier division that lines up exactly with a main-scale mark.
Why is the vernier scale worth reading carefully?
Each small division can represent a tiny fraction of a millimetre, so a single misread line changes the answer. Always check which line lines up exactly with a main-scale mark.
Related topics in Measurement & Math Tools
Prefixes (milli, kilo, mega) · Scientific notation · Length measurement · Screw gauge · Measuring time · Mass vs weight