Session Volume (S_VOL)
This is the total volume accumulated since the start of the session. For example, in the first 10 minutes of trading the volume is 55 and the second 10 minutes it is 20, the session volume will be 55 for the first bar and 75 for the second bar. This continues to accumulate until the end of the session and then resets to zero at the beginning of the next session. Sessions can be the predefined exchange and primary session or any custom session.