The Sorting window allows you to set the options for how your data is sorted.

Sorting Window

Sort Values?

Check this box to sort your data before plotting.  Uncheck it to turn off all sorting.

Ascending / Descending

This specifies the order in which the data should be sorted.

Missing Data

If you are plotting several data sets and one of them is shorter than the others, this option allows you to place the "missing" data at the beginning or end of the plot.