Key relationship
Indicated reading = main scale + coinciding division × least count. Corrected reading = indicated reading − zero error.
Physics · Practical apparatus
Vernier caliper
A vernier compares two scales with slightly different divisions. Ten vernier divisions span nine millimetres, so adjacent divisions differ by 0.1 mm. The coinciding line identifies the fractional part of a millimetre. A positive zero error makes the indicated value too large; subtract it.
Open the interactive experiment →Read the scale between the scale marks.
வெர்னியர் அளவுகோலில் பொருந்தும் கோட்டின் எண்ணை மீச்சிற்றளவால் பெருக்கி முதன்மை அளவுடன் சேர்க்க வேண்டும். பூஜ்யப் பிழையை அளவீட்டிலிருந்து கழிக்க வேண்டும்.
Key notes, relationships and model limits
Practical tip
A vernier compares two scales with slightly different divisions. Ten vernier divisions span nine millimetres, so adjacent divisions differ by 0.1 mm. The coinciding line identifies the fractional part of a millimetre. A positive zero error makes the indicated value too large; subtract it.
Common trap
A positive zero error is subtracted, not added.
Model limits
Ideal outer-jaw, inner-jaw and depth-rod measurement with 1 mm main divisions. The jaw/rod travel is rounded to the nearest vernier division. The expanded scale shows the actual coincidence. Known zero error is subtracted; the remaining rounding bound is ± half the least count. Correct alignment and contact are assumed; jaw wear, force and parallax are outside this model.
What you will learn
Read main and vernier scales; calculate least count; correct signed zero error.
Try the experiment
Change the jaw opening. Identify the highlighted coinciding line, then introduce a known zero error and compare the corrected value.
Think of it this way
Two slightly different combs reveal a fine shift by which pair of teeth lines up.
Worked example
For 10 vernier divisions: least count = 1 − 9/10 = 0.1 mm. Main scale 23 mm plus coincidence 4 gives 23.4 mm.
Why this matters
Fine resolution and zero correction solve different problems; a finer scale cannot remove a calibration error.
Before you start
Decimals · least count · signed errors
Check your understanding
A caliper indicates 23.6 mm with a +0.2 mm zero error. What is the corrected reading?
- 23.8 mm
- 23.4 mm
- 23.6 mm
Read the explanation
Corrected = indicated − zero error = 23.6 − 0.2 = 23.4 mm.
Course connection: Practical apparatus preparation: CBSE XI, NEET/Main experimental skills and JEE Advanced General. Switch outer jaws, inner jaws or the depth rod to prepare different measurement tasks.