Zero Error – Screw Gauge
6 Minutes
Zero error in vernier calipers for students explains positive and negative zero errors and how to correct them. An English physics lesson.
- Why zero errors occur in vernier calipers
- Calculating and correcting positive and negative zero errors
- Using digital vernier calipers to avoid manual error checks
What this lesson teaches
A zero error is an instrument error that occurs when the fixed jaw and movable jaw of a vernier caliper are closed together, but the main scale and the vernier scale do not coincide exactly. If the zero marks fail to line up, the instrument will record an incorrect measurement that is either larger or smaller than the real dimensions of an object.
Checking for errors and why they form
- Errors can form when a manufacturer finishes and assembles all the parts of the instrument.
- Repeatedly using an instrument can cause a screw to become loose, producing errors.
- A user checks for zero error by bringing the fixed jaw and movable jaw completely together.
- If the main scale reading and the vernier scale reading match up perfectly, there is no zero error.
- If the vernier scale sits slightly ahead or behind the main scale zero, an error exists.
Positive zero error and correction
When the vernier scale sits behind the main scale zero mark, the tool has a positive zero error. To find this error, identify the coincident division on the vernier scale by counting from the front and multiply that number by the least count of 0.01 centimeters. For example, if the coincidence occurs at division 5, multiplying it by 0.01 gives a positive error of 0.05 centimeters. Because the instrument records a reading before measuring an object, this positive error must be subtracted from the final measured value.
Negative zero error and correction
A negative zero error happens when the vernier scale sits ahead and starts before the zero of the main scale. To calculate a negative error, the coincident division cannot simply be taken as read, but must be counted backward from the end of the scale. For example, if alignment happens at the eighth division, counting from the end gives a value of 2, which multiplied by the least count of 0.01 centimeters equals 0.02 centimeters. This negative error must be added to the measured value to give the correct size.
Digital vernier calipers
Modern digital vernier calipers eliminate measurement discrepancies and manual calculation errors by displaying the final reading directly on a screen. Users do not need to inspect the alignment of scale divisions or check whether the tool has a positive or negative zero error. The digital display provides the exact measurement immediately, preventing the mistakes that happen when people forget to add or subtract error values.