Kenny posted about it and explained it today. I'll steal his wording cause I'm lazy.
" This signal is rare and indicates a rather large move ahead. The Breadth Thrust Indicator is another momentum indicator. Developed by Martin Zweig, you calculate it by dividing the quantity of advancing issues by the quantity of advancing plus declining issues, and creating a 10 day moving average of the resulting percentage. Having calculated it, you use it if, during any 10 day period, the indicator rises from below 40% to above 61.5%. This is supposed to indicate that the market has moved from an oversold condition to one of strength (but is still not overbought). It fires rarely (the inventor says only 14 times in the last 50 years), and often seems to herald the start of a new bull market. As it fires so rarely, it is not much use when day trading the markets, but if you DO want to use it, take a 10 day moving average of (Advancing Issues) / (Advancing + Declining Issues). You can find this indicator with ready made 40 and 61.5 lines on Think or Swim's Java chart platform."
Apparently the last time it fired was in 1984 and then early this March. Here is the indicator which is available as a technical study under TOS.
I hadn't known about this until Johnny Blue told me about it in comments. The funny thing is the indicator didn't "officially" fire until the 17th of March (maybe the 18th). On the 12th of March I had emailed Kenny back and forth about six times as we discussed that there was a good chance Primary wave 1 had ended at 666. The 12th of March was the day the rally was in its 4th day and it had just breached 750 for the first time as it was coming out of the sub 700 zone. However breadth and volume was easily seen on the indexes and I believe the 12th was the second 90% up day which usually marks a trend change.
That night Kenny declared P1 over and P2 upon us. I was willing to follow Elliott Wave International's count for awhile as they still hadn't given up hope of a 5 of (5). My "uncle" spot was about the 780 mark as I had been calling for a rally to 775 possibly. So 775 came and all was well. Ironically that was on the 17th right at the spot where the Breadth Indicator was just beginning to cross the 61.5 line. On the 18th the SPX pushed up to 800 and that night I of course jumped on the P2 bandwagon officially.
So Kenny confirmed P2 4 days into the rally on the 12th of March when the market just breached 750 5 days prior to the Zweig indicator firing. In retrospect I should have too. I expressed reservations about a (4) of 5 from the 12th to the 17th. I allowed my 780 max retrace target to be hit.
And then my second mistake was assuming a 38% correction would come during this P2 rally. It never did. P2 seems to be on a singular mission and it has a sense of urgency about it. It may still correct 38% but that would probably have to start this week. I don't get hung up about it anymore. Also the 200DMA. It will hit it that much is obvious.
I no longer assume anything. P2 could trace to 1100 (50% retrace) for all I know. After all, its hard to gauge when social mood is ready to let it all go again on the next correction downward.