Cumulative Volume v3

The script, for Pine Script version 3, shows how to accumulate volume values during a defined session/period.

The input is the period to use for accumulation. "D" is the default value, useful to view data for each session.

This is slower than version 4 because there is no "var" and you need to use a loop. Also, you can't use "sum( volume , cnt_new_day)" with a variable length argument instead of "for".