From the reference manual...
No Accumulation
If this option is selected, the y-values of the selected chart expression will not be accumulated.
Full Accumulation
If this option is selected, each y-value will accumulate all previous y-values of the expression. See above under Accumulation.
Accumulate n Steps Back
By entering a number in the box, you set the number of y-values in the expression to be accumulated. See above under Accumulation.
Regards,
Pradeep
