The Delta per bar pane shows how much was bought at market above what was sold on futures in each bar. The header has a “$ / z” unit switch.
Dollars show absolute strength. z expresses the same delta in standard deviations from the last 50 bars: 0 is an ordinary bar, ±2 and beyond is rare. Use z to compare coins and hours with different activity: a million dollars means one thing on BTC and another on a small coin, while z is comparable. z needs at least 20 bars; until then the pane says data is accumulating.