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When both jaws of a vernier callipers touch, the vernier zero is to the right of the main scale zero and the 4th vernier mark coincides with a main scale mark. Measuring a cylinder, 15 divisions are seen on the main scale and the 5th vernier division coincides. The measured length is ______ mm. (Least count =0.1 mm)

Asked in JEE Main 22nd Jan 1st Shift 2025 · Positive zero error

• (1) 15.4
• (2) 15.9
• (3) 15.5
• (4) 15.1

Step-by-step solution

Why the other options are wrong

• (1) Adds the 0.4 mm zero error to 15 and forgets the 0.5 mm vernier reading.
• (2) Adds the zero error instead of subtracting: 15.5+0.4.
• (3) Gives the raw observed reading 15.5 mm without correcting for the positive zero error.

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