What it is
On-balance volume is a running total. Add the day's volume when the stock closes up. Subtract it when the stock closes down. The size of the line has no meaning by itself. Its direction does. OBV rising while the price goes sideways means shares are being bought on the up days faster than they are sold on the down days. The price usually catches up.
How Breakaway uses it
OBV+ fires when on-balance volume is at a 20-day high. It counts on the finished day: during the session it keeps the last close's answer. It is a buying check, which means it tracks steady buying. The card calls it OBV divergence when it is lit. A divergence means OBV is at a high while the price is not.
How to read it
OBV+ with the price also at a high confirms the move. OBV+ with the price below its recent high is the divergence worth studying, because someone is buying the dips. Pair it with a quiet range and you are looking at a base being built. The reverse is a warning. A price at a high while OBV lags means the move is thin.