How To Read A Vernier Caliper - Mini Physics

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  2. / O Level
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  4. / How To Use Calipers (Digital + Vernier)
How To Use Calipers (Digital + Vernier) Show/Hide Sub-topics (Measurement | O Level Physics)
  1. Base Quantities & SI Units
  2. Prefixes
  3. Scalar & Vector Quantities
  4. Vector Addition (Graphical Method)
  5. Measurement Of Length
  6. Measurement Of Time
  7. How To Read A Vernier Caliper
  8. How To Read A Micrometer Screw Gauge
  9. Accuracy, Precision & Measurement Errors
  10. Practice On Reading A Vernier Caliper
  11. Practice On Finding The Zero Error Of A Vernier Caliper
  12. Practice On Reading A Vernier Caliper With Zero Error
On this page
  • 1. Definition
  • A. Digital caliper (recommended)
  • B. Vernier caliper (vernier scale) (optional / legacy)
  • 2. Key Ideas
  • 3. Detailed Explanations
  • A. Digital caliper workflow (quick)
  • B. Vernier caliper scales (optional / legacy)
  • C. Reading a vernier caliper (no zero error)
  • D. Correcting for zero error (works for positive and negative)
  • E. Avoiding parallax (vernier)
  • 4. Common Mistakes
  • A. Reading errors
  • B. Practical technique errors
  • 5. Exam Tips
  • A. What to write for full marks
  • 6. Worked Examples
  • A. Read the main scale and vernier scale (no zero error)
  • B. Correct a zero error using the closed-jaws reading
  • C. Correct a positive zero error
  • D. Digital caliper (unit conversion)
  • E. Digital caliper zero error correction
  • 7. Mind Stretchers
  • A. Why is zero error a systematic error?
  • B. Choosing better technique
  • 8. Practice

1. Definition

A digital caliper measures internal diameters, external diameters, and depths, and displays the reading directly (usually in mm).

B. Vernier caliper (vernier scale) (optional / legacy)

A vernier caliper is an analogue caliper that uses a main scale and a vernier scale to read lengths to a fine resolution (commonly ).

2. Key Ideas

  • Digital caliper: close → ZERO → measure gently → record the display value with units.
  • Vernier caliper:
    • Observed reading main scale reading vernier reading.
    • Corrected reading observed reading zero error.
  • Avoid parallax: read the scale straight-on, not at an angle.
  • Record to a sensible precision (match the instrument’s resolution).

3. Detailed Explanations

A. Digital caliper workflow (quick)

  1. Close the jaws gently and press ZERO (make sure the jaws are clean).
  2. Select units (mm).
  3. Use the correct part:
    • outside jaws: external diameter / thickness
    • inside jaws: internal diameter
    • depth rod: depth
  4. Record the displayed value with units (e.g. 12.34 mm).

If it won’t zero, treat the offset as a zero error and correct for it (same idea as vernier): see Accuracy, Precision & Measurement Errors.

B. Vernier caliper scales (optional / legacy)

Optional / legacy

Most practicals use digital calipers, but the vernier scale method still appears in questions. The steps below are for vernier-scale calipers (no digital display).

Vernier caliper main scale and sliding vernier scale; read the main scale then the aligned vernier division
Read the main scale first, then find the vernier line that aligns exactly.

C. Reading a vernier caliper (no zero error)

  1. Main scale reading: the value on the main scale immediately to the left of the vernier zero.
  2. Vernier reading: find the vernier division that lines up exactly with a main-scale line.
  3. Add: observed reading main scale vernier reading.

Mini-example:

Example vernier reading: main scale 2.1 cm with the 3rd vernier division aligned (observed 2.13 cm)
Example: main scale = 2.1 cm, vernier = 0.03 cm, so observed reading = 2.13 cm.

D. Correcting for zero error (works for positive and negative)

Use one rule for both signs:

Zero-error correction rule
  • Positive zero error: vernier zero is to the right of main zero.
  • Negative zero error: vernier zero is to the left of main zero.

Mini-example: observed reading , zero error .

Correct reading .

E. Avoiding parallax (vernier)

  • Put your eye directly above the scale line you’re reading.
  • Make sure the jaws touch the object gently and squarely (don’t tilt the caliper).

4. Common Mistakes

A. Reading errors

  • Taking the main-scale value to the right of the vernier zero (it should be to the left).
  • Choosing a line that “almost” aligns; select the one that aligns best.
  • Forgetting to correct for zero error when it is given.

B. Practical technique errors

  • Viewing at an angle (parallax error).
  • Squeezing the object (especially soft materials), changing the size.
  • Recording without units or using the wrong unit (cm vs mm).

5. Exam Tips

A. What to write for full marks

  • Show the method:
    • main scale reading
    • vernier reading (include least count)
    • observed reading
    • corrected reading (if there is zero error)
  • Use the exact wording: “correct reading observed zero error”.
  • Quote values to the correct resolution (often for vernier scale questions).

6. Worked Examples

A. Read the main scale and vernier scale (no zero error)

Example vernier reading: vernier zero just past 10.0 cm with the 2nd vernier line aligned (observed 10.02 cm)
Find the observed reading from the vernier caliper.
Click here to show/hide answer
  • Main scale reading (immediately left of the vernier zero).
  • Vernier reading .
  • Observed reading .

B. Correct a zero error using the closed-jaws reading

Vernier caliper showing an observed reading and a closed-jaws reading (zero error); correct reading = observed − zero error
The top reading is the observed measurement; the bottom reading shows the zero error when the jaws are closed.

Observed reading , zero error .

Click here to show/hide answer

Correct reading .

C. Correct a positive zero error

Observed reading , zero error .

Click here to show/hide answer

Correct reading .

D. Digital caliper (unit conversion)

A digital caliper reads 12.34 mm. State the length in centimetres.

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.

E. Digital caliper zero error correction

A digital caliper reads when closed. It measures a thickness as . Find the corrected thickness.

Click here to show/hide answer

7. Mind Stretchers

A. Why is zero error a systematic error?

A student forgets to correct for a constant zero error when measuring the diameter of a wire.

  1. Is the error random or systematic?
  2. How does it affect accuracy and precision?
Click here to show/hide answer
  • It is a systematic error because every reading is shifted by the same amount.
  • Accuracy becomes worse (all readings are too large or too small).
  • Precision can still be good (readings may be tightly clustered).

B. Choosing better technique

Two students measure the same rod with a vernier caliper:

  • Student A squeezes hard until the jaws “bite”.
  • Student B closes gently, checks for dirt, and reads at eye level.

Whose result is more reliable, and why?

Click here to show/hide answer
  • Student B’s result is more reliable.
  • Gentle contact avoids deforming the object and reduces inconsistent pressure.
  • Eye-level reading reduces parallax error.

8. Practice

Practice Time! Go to Measurement Quiz

Vernier practice:

  • Practice: Reading a Vernier Caliper
  • Practice: Finding Vernier Zero Error
  • Practice: Vernier Reading with Zero Error

Related lesson:

  • Accuracy, Precision & Measurement Errors

Optional external simulator:

  • Vernier Caliper Simulation
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