This is the NYSE Advancers - decliners which the SPX pretty much follows. You can chart it like any index (ADD -NYSE AADV MINUS DDECL) but I find it more useful in a separate panel with colors for direction.
The level gives an idea of days move (example: plus or minus 500 is not much movement through the session) but I follow the direction as when more stocks advance (green) or decline (red) the index tends to track it pretty closely.
On SPX, SPY and correlateds - very useful for intra-day trading (Scalping or 0DTE option trades) but not for higher time frames at all. If you chart the ADD in a chart and compare 5 minute to daily you will see what I mean.
I left it at 5 minutes timeframe which displays well on any intraday chart. You can change it by changing the "5" in the security function on line 13 to what you want ("1" 1 minute, "15" 15 minutes) or change it to timeframe.period (no quotes) so that it will follow the timeframe of the current chart. I like 5 min as it displays better on higher timeframes i.e. 15 min. or hour. A simple moving average with a length of 10 is added to help gauge momemtum.
Hope this helps with trading or scripting ideas, questions or feed back welcome. Keep Smiling.