This document discusses how to identify and account for zero error when using micrometers and vernier calipers. It explains that a micrometer has positive zero error if the zero marking is below the datum line, and negative zero error if above, and in either case the zero error value must be subtracted from readings. Vernier calipers also require identifying and subtracting any zero error based on the misalignment of the zero marking and datum line.

1. Reading Micrometer and
Vernier Calipers

2. Micrometer

5. Zero Error for Micrometer
No zero error

6. This micrometer has zero error.
The zero marking on the thimble is below the datum line. So this micrometer
has a positive zero error.
How do we count the zero error?
In this case we will take the reading on the thimble.
Thimble reading = 0.03 mm
So the micrometer has a zero error of +0.03 mm.
Whatever reading we take on this micrometer we would have to
subtract +0.03 mm

7. The zero marking on the thimble is above the datum line. So this micrometer
has a negative zero error.
In this case we will have to count the number of divisions on the thimble
between the zero marking and the datum line.
No. of divisions = 3
Measurement of each division = 0.01mm
So the micrometer has a zero error of -0.03 mm.
Whatever reading we take on this micrometer we would have to
subtract -0.03 mm

8. Vernier Calipers