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Practice On Reading A Vernier Caliper With Zero Error

Key idea: Practice vernier readings with zero error: find the zero error and corrected readings with worked answers for O Level Physics practical-style questions.

  • G3 Physics topic extensions
On this page

Learning objectives

  • Read an analogue vernier caliper scale and correct the reading for zero error

1. Definition

A. What you are practising

Each image shows two readings:

  • top: jaws closed (this is the zero error)
  • bottom: jaws on an object (this is the observed reading)

Find the zero error and the correct reading.

If you need a refresher, use: How To Use Calipers (Digital + Vernier) and Accuracy, Precision & Measurement Errors.

2. Key Ideas

  • Use one rule for both signs: correct reading = observed reading - zero error.
  • Positive zero error: vernier zero is to the right of main zero.
  • Negative zero error: vernier zero is to the left of main zero.

3. Detailed Explanations

A. Quick workflow

  1. Read the zero error from the top scale (include sign).
  2. Read the observed reading from the bottom scale.
  3. Subtract: correct = observed - zero error.

4. Common Mistakes

A. Typical slips

  • Subtracting the wrong way (especially with negative zero error).
  • Copying the magnitude but missing the sign.
  • Forgetting the unit.

5. Exam Tips

A. Write one clear line

Always write the correction explicitly (with brackets):

correct = (observed) - (zero error)

5A. Interactive Trainer

Use this before the fixed worked set

Train with randomised zero-error cases first, then use the static set below to practise clean written working.

Simulation Trainer: Vernier Zero Error + Correction

Use the top closed-jaws scale to find zero error, then correct the observed reading from the bottom scale.

BetaO LevelA LevelPractical SkillsBest for: O Level and H2 learners losing marks on correction sign
  • Zero-Error Sign
  • Zero-Error Magnitude
  • Corrected Reading

Open the full interactive simulation on its own page

Use the standalone simulation page for the live controls, SVG scene, run modes, and scoring flow.

Open Interactive Simulation

The lesson stays lightweight and links out to the dedicated simulation page.

After this trainer
  1. Measurement Quiz
  2. Structured Measurement
  3. Practice: Reading a Vernier Caliper
  4. Practice: Finding Vernier Zero Error

6. Worked Examples

Modelled example 1

Question 1 — model the full correction

Core

Problem

Find the signed zero error, observed reading and corrected reading.
Vernier corrected-reading question 1Top: jaws closed: with the jaws closed, vernier zero lies to the left of main zero, and vernier division 7 aligns with a main-scale line. Bottom: object reading: the main-scale value immediately left of vernier zero is 0.0 centimetres, and vernier division 6 aligns with a main-scale line.Top: jaws closedmain scale (cm)01vernier scale0510best alignmentBottom: object readingmain scale (cm)0.01.0vernier scale0510best alignment
Study the worked solution

  1. Read the zero error

    Method

    e₀ = -0.03 cm.

    Reason

    Vernier zero is left of main zero; division 7 aligns, leaving three least counts.

    Working

    e₀ = -(10-7)(0.01) = -0.03 cm

  2. Read the object

    Method

    x_observed = 0.06 cm.

    Reason

    The main scale is zero and division 6 contributes 0.06 cm.

    Working

    0.0 + 6(0.01) = 0.06 cm

  3. Apply the signed correction

    Method

    x_correct = 0.09 cm.

    Reason

    Correct reading equals observed minus the signed zero error.

    Working

    0.06-(-0.03) = 0.09 cm

Guided practice 2

Question 2 — positive-error correction

About 4 min

Problem

Find the corrected reading in centimetres.
Vernier corrected-reading question 2Top: jaws closed: with the jaws closed, vernier zero lies to the right of main zero, and vernier division 3 aligns with a main-scale line. Bottom: object reading: the main-scale value immediately left of vernier zero is 1.0 centimetres, and vernier division 6 aligns with a main-scale line.Top: jaws closedmain scale (cm)01vernier scale0510best alignmentBottom: object readingmain scale (cm)1.02.0vernier scale0510best alignment

Try this before viewing the solution

Unit: cm

Hints

Hint 1: write three lines
Record e₀, then x_observed, then use x_correct = x_observed-e₀.
View solution step by step

  1. Read both scales

    Method

    e₀ = +0.03 cm and x_observed = 1.06 cm.

    Reason

    Top division 3 gives the positive error; bottom division 6 adds 0.06 cm to 1.0 cm.

    Working

    e₀ = +3(0.01); x_observed = 1.0 + 6(0.01)

  2. Correct

    Method

    x_correct = 1.03 cm.

    Reason

    A positive zero error makes the observed reading too large.

    Working

    1.06-(+0.03) = 1.03 cm

Common misconception 3

Question 3 — subtracting a negative

Find and correct the mistake

Learner claim

A learner reads -0.06 cm zero error and 6.43 cm observed, then calculates 6.43-0.06 = 6.37 cm. Diagnose the correction.
Vernier corrected-reading question 3Top: jaws closed: with the jaws closed, vernier zero lies to the left of main zero, and vernier division 4 aligns with a main-scale line. Bottom: object reading: the main-scale value immediately left of vernier zero is 6.4 centimetres, and vernier division 3 aligns with a main-scale line.Top: jaws closedmain scale (cm)01vernier scale0510best alignmentBottom: object readingmain scale (cm)6.47.4vernier scale0510best alignment

Try this before viewing the solution

Unit: cm

View solution step by step

  1. Retain the signed error

    Method

    Use e₀ = -0.06 cm, not merely its magnitude.

    Reason

    The correction rule subtracts the signed zero error.

    Working

    x_correct = x_observed-(-0.06)

  2. Resolve the double sign

    Method

    Subtracting the negative error adds 0.06 cm.

    Reason

    -(-0.06) = +0.06.

    Working

    6.43-(-0.06) = 6.43 + 0.06

  3. Correct the result

    Method

    x_correct = 6.49 cm.

    Reason

    The negative zero error made the observed reading too small.

    Working

    6.43 + 0.06 = 6.49 cm

Examiner practice 4

Question 4 — given negative error

3 marks

Examination question

Observed reading is 2.36 cm and zero error is -0.04 cm. Find the correct reading. [3 marks]

Try this before viewing the solution

Unit: cm

View solution step by step

  1. State the rule

    1 mark

    Method

    Correct equals observed minus zero error.

    Reason

    The rule is valid for either error sign.

    Working

    x_correct = x_observed-e₀

  2. Substitute signs

    1 mark

    Method

    x_correct = 2.36-(-0.04).

    Reason

    The negative sign belongs inside the substitution.

    Working

    2.36-(-0.04) = 2.36 + 0.04

  3. Calculate

    1 mark

    Method

    x_correct = 2.40 cm.

    Reason

    Adding four hundredths corrects the under-reading.

    Working

    2.36 + 0.04 = 2.40 cm

Challenge 5

Question 5 — reverse the error sign

Minimal support

Independent transfer

Observed reading is 7.65 cm and zero error is + 0.01 cm. Find the correct reading.

Try this before viewing the solution

Unit: cm

Hints

Hint 1: keep one universal rule
Use x_correct = x_observed-e₀; do not memorise a separate sign rule.
View solution step by step

  1. Substitute the positive error

    Method

    x_correct = 7.65-(+0.01).

    Reason

    The signed zero error is positive.

    Working

    x_correct = 7.65-(+0.01)

  2. Calculate

    Method

    x_correct = 7.64 cm.

    Reason

    A positive zero error makes the observed value too large, so the correction reduces it.

    Working

    7.65-0.01 = 7.64 cm

7. Mind Stretchers

Mind stretcher 1: Negative zero error intuitionExtension

If the zero error is negative, do you add or subtract its magnitude to get the correct reading? Explain.

Show Answer

You add its magnitude, because subtracting a negative is addition:

correct = observed - (negative) = observed + |zero error|

Mind stretcher 2: Systematic vs randomExtension

Why does a constant zero error count as a systematic error?

Show Answer

It shifts every reading by the same amount in the same direction, so the error is consistent (systematic).

Continue with the next resource in this course.

Course and syllabus information
Course
G3 Physics topic extensions
Syllabus scope
Beyond the syllabus
Edition
G3 Physics topic extensions