Happy Birthday Hot 100

This week's issue of Billboard celebrates the 50th anniversary of the publication's most prominent char, the Hot 100, a weekly tabulation of the most popular songs in the United States based on airplay and sales. The formula has changed through the years, accommodating changes in media formats and more recently what "airplay" means, but it remains the best national barometer of popular music.

The issue has a lot of special charts and articles, including a new "definitive" list of the top Hot 100 hits of the last 50 years. A great improvement in this chart over previous such charts--it's been weighted to take into account periods when chart turnover increases or decreases. This was a problem with some of the previous methodologies, where you'd see, for example, lots of entries from the mid '90s when the chart slowed down (so songs stayed around a long time racking up chart "points") and very few from 1987-1991 (when songs rotated through the chart much faster).