Chaikin money flow

Whether recent volume closed mostly near bar highs or bar lows, from -1 (lows) to +1 (highs).

Chaikin money flow scores each bar by where its close sits inside that bar's high-low range: +1 at the high, -1 at the low, 0 mid-range. It weights each score by the bar's volume, then divides the total over the last N bars by the total volume over the same bars. Near +1 means heavy volume closed near the highs (accumulation); near -1 means heavy volume closed near the lows (distribution).

How to read it

The line sits in its own pane below the price, always between -1 and +1.
Above zero, recent volume leaned toward closes near the highs; below zero, toward closes near the lows.
On SPY one-minute bars at the default 20, readings beyond ±0.5 happen about one bar in ten, so a strong reading alone is not a signal.
The classic warning is a new price high that the line fails to match; treat it as a convention, not a proven signal.

What it outputs

CMF: Volume-weighted share of recent closes near highs versus lows, between -1 and +1.

Settings

Window: How many recent bars the sums cover, the current one included. Shorter follows the last few minutes and swings toward the extremes often; longer averages more bars, moves slowly, and is less likely to reach ±0.5.

Pitfalls

Volume-weighted: one heavy bar can move the line more than several quiet ones. When it jumps, check that bar's volume first.
Zero-range bars (high equals low) score 0 but still add their volume to the total, pulling the line toward zero. A window with no volume reads 0, which looks like balance rather than missing data.
It describes where closes sat inside their ranges, not where price is heading. On SPY one-minute bars its correlation with price level is near zero, so do not read it as a trend line.