On-balance volume
A running sum of volume: an interval's volume is added when it closes above the previous one and subtracted when it closes below.
How to read the number
The line shows on which side traded volume accumulated and is read together with price; the height of the line on its own carries no meaning.
When the metric lies
The sign of the contribution is decided by the close, so a single trade just before the bell flips the contribution of the entire day's volume to the opposite side.
Also known as: obv