Basically, whenever the ATR _percent line leaves the yellow line for upwards, market is falling. While if it is heading downwards, the market is rising.
In true TradingView spirit, the author of this script has published it open-source, so traders can understand and verify it. Cheers to the author! You may use it for free, but reuse of this code in a publication is governed by House Rules. You can favorite it to use it on a chart.