From some deduction, I see that it was basically looking at the ratio of down by up on the NYSE exchange; he had a few levels marked as well (which I've also marked on this indicator).
Seems like an interesting metric to consider, basically used to get a rough idea of the short term sentiment of the masses; allowing one to see when selling is outpacing buying in pure traded on an exchange.
I've added a few other exchanges to allow for quick switch between the majors with this info readily available on TradingView.
Supported inputs are: AMEX, NYSE, NASDAQ, ALL (must be in caps)
All is the sum of the NYSE, AMEX, and NASDAQ exchange .
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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.