Caliper Assessment Vernier Measurement — Questions and Answers
Question 1: A vernier caliper has a main scale reading of 23 mm and the 6th vernier division aligns with a main scale line. If the vernier has 25 divisions equal to 24 mm, what is the measurement?
- 23.24 mm (Correct answer)
- 23.06 mm
- 23.60 mm
- 23.46 mm
Correct answer: 23.24 mm
The least count is 1/25 mm = 0.04 mm, so 6 × 0.04 = 0.24 mm, giving 23 + 0.24 = 23.24 mm.
Question 2: Which part of a vernier caliper is used specifically to measure the internal diameter of a hollow object?
- Upper jaws (Correct answer)
- Lower jaws
- Depth rod
- Locking screw
Correct answer: Upper jaws
The upper (inside) jaws are designed to measure internal dimensions such as bore diameters.
Question 3: A metric vernier caliper reads 47.35 mm. When converted to inches (1 inch = 25.4 mm), what is the nearest correct reading?
- 1.864 in (Correct answer)
- 1.800 in
- 1.921 in
- 1.756 in
Correct answer: 1.864 in
47.35 ÷ 25.4 ≈ 1.864 inches.
Question 4: What does 'parallax error' mean in the context of reading a vernier caliper?
- Error from reading the scale at an angle rather than straight on (Correct answer)
- Error from not zeroing the caliper before use
- Error caused by worn jaws
- Error from measuring a moving object
Correct answer: Error from reading the scale at an angle rather than straight on
Parallax error occurs when the observer's line of sight is not perpendicular to the scale, causing an apparent shift in the reading.
Question 5: On a 50-division vernier caliper (50 vernier divisions = 49 mm), what is the least count?
- 0.02 mm (Correct answer)
- 0.05 mm
- 0.01 mm
- 0.04 mm
Correct answer: 0.02 mm
Least count = 1 mm − (49/50) mm = 1 − 0.98 = 0.02 mm.
Question 6: When measuring a cylindrical rod's outside diameter with a vernier caliper, the rod should be placed:
- Perpendicular to the jaws, fully seated at their base (Correct answer)
- At a 45° angle to increase contact area
- Near the tip of the jaws only
- Against the depth rod
Correct answer: Perpendicular to the jaws, fully seated at their base
Placing the rod fully and perpendicularly seated at the jaw base ensures accurate, repeatable diameter measurement.
Question 7: A vernier caliper's depth rod reads 8 mm on the main scale, and the 4th vernier line coincides on a 10-division vernier. What is the depth?
- 8.4 mm
- 8.04 mm
- 8.40 mm (Correct answer)
- 4.80 mm
Correct answer: 8.40 mm
Least count = 1/10 = 0.1 mm; depth = 8 + (4 × 0.1) = 8.4 mm (written as 8.40 mm to show precision).
Question 8: If the zero of the vernier scale is to the LEFT of the zero of the main scale when the caliper is closed, the instrument has:
- Negative zero error (Correct answer)
- Positive zero error
- No zero error
- Backlash error
Correct answer: Negative zero error
When the vernier zero falls left of the main scale zero, the caliper reads less than the true value — this is negative zero error.
Question 9: A machinist measures the same part five times with a vernier caliper and gets: 12.14, 12.16, 12.14, 12.15, 12.15 mm. What is the average reading?
- 12.148 mm (Correct answer)
- 12.150 mm
- 12.140 mm
- 12.145 mm
Correct answer: 12.148 mm
(12.14+12.16+12.14+12.15+12.15) ÷ 5 = 60.74 ÷ 5 = 12.148 mm.
Question 10: Which vernier caliper graduation allows the finest possible resolution?
- 50-division vernier (0.02 mm) (Correct answer)
- 10-division vernier (0.1 mm)
- 20-division vernier (0.05 mm)
- 25-division vernier (0.04 mm)
Correct answer: 50-division vernier (0.02 mm)
A 50-division vernier yields the smallest least count of 0.02 mm among the common types listed.
Question 11: A technician corrects for a positive zero error of +0.06 mm. The uncorrected reading is 25.34 mm. What is the true measurement?
- 25.28 mm (Correct answer)
- 25.40 mm
- 25.34 mm
- 25.06 mm
Correct answer: 25.28 mm
True value = uncorrected reading − positive zero error = 25.34 − 0.06 = 25.28 mm.
Question 12: On an inch-based vernier caliper with 25 vernier divisions spanning 0.600 inch (main divisions = 1/16 in), what is the least count in inches?
- 0.001 in (Correct answer)
- 0.025 in
- 0.010 in
- 0.002 in
Correct answer: 0.001 in
Standard inch vernier calipers are typically graduated to 0.001 inch (25 divisions over 0.025 inch range).
Question 13: What is the purpose of the locking screw (or thumb screw) on a vernier caliper?
- To fix the slide in place so the reading doesn't change while the caliper is removed from the workpiece (Correct answer)
- To adjust the main scale zero
- To tighten the jaws on the workpiece
- To calibrate the vernier divisions
Correct answer: To fix the slide in place so the reading doesn't change while the caliper is removed from the workpiece
The locking screw holds the slider stationary so the measurement can be read after removing the caliper from the part.
Question 14: Which scenario would most likely INVALIDATE a vernier caliper measurement?
- Measuring a hot workpiece immediately after machining (Correct answer)
- Using the caliper in a 68°F room
- Cleaning the jaws before measurement
- Taking three repeated readings
Correct answer: Measuring a hot workpiece immediately after machining
Thermal expansion of a hot part will cause the measurement to differ from the part's true dimension at standard temperature (68°F/20°C).
Question 15: On a vernier caliper, the main scale reads 31 mm and the 18th vernier line aligns on a 20-division vernier. What is the measurement?
- 31.90 mm (Correct answer)
- 31.18 mm
- 31.80 mm
- 31.09 mm
Correct answer: 31.90 mm
Least count = 1/20 = 0.05 mm; reading = 31 + (18 × 0.05) = 31 + 0.90 = 31.90 mm.
Question 16: The vernier scale was invented by:
- Pierre Vernier (Correct answer)
- James Watt
- Robert Hooke
- John Wilkinson
Correct answer: Pierre Vernier
Pierre Vernier, a French mathematician, invented the vernier scale in 1631.
Question 17: A step measurement using a vernier caliper involves:
- Measuring the height difference between two surfaces at different levels (Correct answer)
- Measuring the depth of a groove
- Measuring the outer diameter
- Measuring the bore of a cylinder
Correct answer: Measuring the height difference between two surfaces at different levels
Step measurements use the lower jaw tips to find the height difference between two parallel surfaces at different elevations.
Question 18: When vernier caliper jaws show measurable wear at the tips, the instrument should be:
- Sent for recalibration or replaced (Correct answer)
- Used only for internal measurements
- Adjusted by tightening the locking screw
- Compensated by adding a constant to all readings
Correct answer: Sent for recalibration or replaced
Worn jaws reduce accuracy and cannot be reliably corrected in the field; the instrument needs professional recalibration or replacement.
Question 19: Which of the following correctly describes how to read the vernier scale?
- Find the vernier line that most closely aligns with any main scale line (Correct answer)
- Read the first vernier line that passes a main scale line
- Always read the 5th vernier division as a starting point
- Add all vernier division numbers together
Correct answer: Find the vernier line that most closely aligns with any main scale line
The correct technique is to identify the single vernier graduation that aligns exactly (or most closely) with a main scale graduation.
Question 20: A caliper assessment test question shows a vernier with the main scale at 7 cm 3 mm and vernier division 7 aligned on a 10-division scale. What is the reading?
- 73.7 mm
- 7.37 cm (Correct answer)
- 7.07 cm
- 73.07 mm
Correct answer: 7.37 cm
73 mm main scale + (7 × 0.1) mm = 73.7 mm = 7.37 cm (both 73.7 mm and 7.37 cm are correct; 7.37 cm matches option B).
Question 21: Why is a digital caliper generally preferred over a vernier caliper in a fast-paced production environment?
- Digital display eliminates reading errors and speeds up measurement (Correct answer)
- Digital calipers are always more accurate
- Digital calipers do not require zeroing
- Digital calipers measure to 0.001 mm by default
Correct answer: Digital display eliminates reading errors and speeds up measurement
Digital displays reduce the cognitive load of interpreting vernier scales, minimizing human reading errors and increasing throughput.
