magazine's weekly pop singles
chart. The chart uses a point system based on radio airplay
From its birth in August of 1959 to November of 1998, only commercially released singles were allowed to enter the chart. Beginning in December of 1998, album tracks were allowed on the chart as well.
For the curious, the longest stay at #1 on the chart was 16 weeks; this record is held by "One Sweet Day" by Mariah Carey and Boyz II Men. The longest stay on the chart was 69 weeks, by "How Do I Live" by LeAnn Rimes.