Whenever a measurement is made there is always some uncertainty about the result. Repeating a measurement and looking at how spread out the readings are lets us estimate how big the uncertainty is.
To do this, find the mean and the range. The mean is the total of the readings divided by the number of readings. The range is the highest value minus the lowest value. A small range means the results are close together. A bigger range means the results are more spread out.
The range about the mean is a measure of uncertainty. Half the range is the uncertainty, and the result is written as the mean ± the uncertainty.
For example, five titration readings are 24.1, 24.3, 24.2, 24.4 and 24.0 cm3. The total is 121.0 cm3, so the mean is 121.0 ÷ 5 = 24.2 cm3. The range is 24.4 − 24.0 = 0.4 cm3. Half the range is 0.2, so the result is 24.2 ± 0.2 cm3. A bigger range gives a bigger uncertainty.