Notating Standard Deviation?

Question

If the standard deviation is 0.45 and the average is 8.79, it can be written as:

8.79 +/- .45 or as 8.79 +/- 8.79%.

Under what conditions would the percentage notation be more useful in respect to experiments?

Answer 1

When the measured value is not the variable whose expected value is given but something proportional to it. For instance if the expected density of a compound is ~8.79 but you are weighing 20 ml of it, the expected weight is 0.02*8.79, and the percentage deviation can be applied directly to the weight measurements.