How is zero error taken into account for getting true reading?

Hint: In this question use the concept that if the pointer of the instrument indicates below zero then it is called as negative zero and if the pointer of the instrument indicates above zero then it is called as positive zero error. This will help take account for getting true reading.

Complete Step-by-Step solution:
Before performing the experiment we have to calibrate the instrument and calculate its zero error.
So if the pointer of the instrument indicates below zero then it is called a negative zero error and we have to add the magnitude of this error in the measured reading of the instrument.
Therefore true reading = measured reading + magnitude of negative zero error.
Now if the pointer of the instrument indicates above zero then it is called a positive zero error and we have to subtract the magnitude of this error in the measured reading of the instrument.
Therefore true reading = measured reading – magnitude of positive zero error.
Now if the pointer of the instrument indicates exactly at zero then it is called a null zero error and in this case measured reading is equal to the true reading of the instrument.
So this is the required answer.

Note – Any indication that a measuring system gives a false reading when the true value of measured quantity is zero, e.g the needle on an ammeter failing to return to zero when no current flows. A zero error may result in a systematic uncertainty.