If you have used vernier caliper then you may be aware that it is initially zeroed to get accurate measurement. But on many occasions negative zero reading occurs, but what does this error mean?
Everyone who used vernier caliper knows that before this precise measurement instrument is used the zero on the main scale is aligned with the zero on the vernier scale. So the default condition for the vernier caliper should be that both zero coincides.
Now there are chances of two types of error, either the zero of the vernier does not reach the main scale or the zero of vernier crosses the zero of main scale. These are called positive zero and negative zero.
It is called positive zero error if the scale is on greater number than zero and called negative when the number is less than zero. In other words if the zero of the vernier caliper crosses the zero of main scale it is called positive zero reading and when it stops before the zero of main scale it is called negative zero reading.
The positive zero error is written with a plus sign (+) while the negative zero reading is symbolized with a minus sign (–).
You can still use the Vernier Caliper with the zero reading error but one more step is added in your measurement process. The error can be overcome by using this formula:
Actual reading = main scale + vernier scale − (zero error)
So if the instrument reads 5.48 cm and the error is +0.05, the actual length will be 5.48-0.05 = 5.43 cm
Why Zero Error Occurs?
Zero error occurs due to knocks which effect the calibration of the vernier caliper when the jaws are closed. By using the simple formula you can get the measurement accurately.
Vernier Caliper is an instrument used for precise measurement of internal and external dimensions, what makes it unique is the more precise readings.
Now modern digital vernier calipers are also being used around the world which are far easier to use than traditional vernier caliper. The zero reading error including negative percent error does not occur in digital vernier calipers.