Question

Which quantity is use to generate the error bars on a graph?

Answer 1

The error bars are used to indicate the variability of the data presented in a graph.

There are several quantities that can be used to generate error bars in the graph. These are:
standard deviation
standard error
confidence interval

Usually, one standard deviation above and below the mean is used although it is advised to indicate which variability data is used to generate the error bars in the graph since the 3 quantity given are not equal.