Who Monitors Radio Stations?

Mediabase 24/7

Mediabase 24/7 uses people to identify how many times a song is played on the radio. Many formats are monitored. Mediabase's main website is password restricted, but you can some information at their website. 

Broadcast Data Systems (BDS)

BDS was a company that electronically monitored radio stations and counts how many times a song is played. This data was used by Billboard and its former sister Airplay Monitor magazines in making charts.