This indicator is based on Volatility and Market Sentiment. When volatility is high, and market sentiment is positive, the indicator is in a low or 'buy state'. When volatility is low and market sentiment is poor, the indicator is high.
The indicator uses the VIX as it's volatility input.
The indicator uses the spread between the Call Volume on SPX/SPY and the Put Volume.
This is pulled from CVSPX and PVSPX.
When volatility and put/call reaches a critical level, such as the levels present in a crisis or a sell off, the line will be green. See Sept 2015, 2008, and Feb 2018.
This level can be edited in the source code.
As the indicator is based on Put/Call, the indicator works best on larger time frames as the put/call ratio becomes a more discernible measure of sentiment over time.