<span>0.833333333333333 is the answer</span>
Since the precision of the voltmeter is <span>±0.005 V, the effective value range for the first measurement is 9.000 V to 9.010 V, for the second it is 9.001 V to 9.010 V, the third 9.013 V to 9.023 V and the fourth 9.021 V to 9.030 V. From all of these measurements the only one which the accepted value falls within the range is measurement 3.</span>
The absolute value function is:

To translate it we need to remember the following rules:
Using this table we conclude that the function we are looking for is: