American Top 40 based on Billboard's Top 100 was based on sales AND airplay thruout the country.BRNout referred to regional hits not charting well nationally.A great example of this was a song that was the #1 song in Boston for 1973,yet only reached #59 nationally that year.After the group had 2 more gold albums,they re-released the single and it would hit #6 on Billboard Magazine's top 100 in April of 1976.In fact,you heard on last Saturday's AT 40 show.It was #16 nationally,with no help from Boston,since everyone here had bought this single 3 years earlier.I think you've heard of' 'Dream On'- Aerosmith.