Getting Started: The zero error
Before measuring the length of any object, make sure that both jaws of the Vernier Caliper are closed and the zero on Vernier Scale coincides with the zero on the main scale. If it doesn't, it is said to have a zero error which needs to be noted down before using the instrument.
Holding the object
If there is no zero error, then start the measurement process. If the diameter of a ball is being measured, the hold it between the lower jaws. If the inner diameter is to be measured, we use the upper jaws.
Look for Zero on Vernier Scale
The first thing to observe is zero's location on the Vernier scale. Upon observing, you will notice that it is lying somewhere between two successive divisions on the main scale.
The correct length calculated
When both the readings are added, the resulting one will be our desired length of the object correct to 0.1mm or 0.01 cm.