Subject: Re: Statistics for Nasdaq 100 monthly Momentum Screen
Just to understand it fully. Are we talking about running the screen monthly or 21 calendar days (3 weeks)??

Market days.
All the standard SMA periods are market days. 200 day SMA, 50 day... all are "trading days"

5 days/week times 4.25 weeks/month = 21.25 days.
Subtract a little bit to account for weekdays where the market is closed is very close to 21.