# When Is Zero Error Positive In Vernier Calipers And When Is It Negative?

Positive zero error is when the jaws are closed and the zero on the vernier scale is to the right of the zero of the main scale.The measurement taken with this pair of vernier calipers will be MORE than the actual result. To get the correct value, the zero error must be subtracted from each reading. Eg: The zero error (0.03) is subtracted from the reading. The actual reading is thus (eg) 2.35-0.03cm= 2.32
Negative error is when the jaws and closed and the zero of the vernier scale is to the left or  the zero of the main scale. The measurement taken with this pair if vernier calipers will be LESS than the actual value. To get the correct value, the numerical value of the zero error must be ADDED to each reading. Eg: The 4th line on the vernier scale is in line with the marking on the main scale. The zero error (0.10-0.04cm=0.06cm) is added to the rading. The actual reading is thus 2.35+0.06cm=2.41
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Zero Errors of Vernier Caliper

When the jaws are closed, the vernier zero mark coincides with the zero mark on its  fixed main scale. Before taking any reading it is good practice to close the jaws or faces of the instrument to make sure it is reading zero. If not then note the reading. This reading is called “zero error”.  The zero error is of two types (I) positive zero error and (ii) negative zero error.

Positive Zero Error
If the zero on the vernier scale is to the right of the main scale, then the error is said to be positive zero error and so the zero correction should be subtracted from the reading which is measured.

Negative Zero Error
If the zero on the vernier scale is to the left of the main scale, then the error is said to be negative zero error and so the zero correction should be added from the reading which is measured.
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When the 0 on the movable scale is BEFORE the 0 on the main scale, it is a negative zero error.
When the 0 on the movable scale if AFTER the 0 on the main scale, it is a positive zero error.
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I found something online that may help you out here --- it also has diagrams of the vernier calipers in positive and negative positions.  The site is:  www.scribd.com

When you're on that page, type "vernier caliper" in the search box at the top right of the pictured report.  It will take you right to the page that shows when the vernier calipers are in positive and negative positions.

Good luck!  If you're taking physics, you're a pretty smart gal!

Moe
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