Breadth is *equal* weight Spx is *market* cap weighted  ie. Calculating breadth $AAPL $AMZN $Msft weight as much as $coty $ua $nws  However, amzn+aapl+Msft weights 16.4% vs coty ua nws 2.5%  If amzn+msft+aapl up but coty ua nws down : breadth =0, but spx strongly up