ZM ( ) is a New Zealand contemporary hit radio network owned by New Zealand Media and Entertainment. It broadcasts 19 markets throughout mainland New Zealand via terrestrial FM, and worldwide via the Internet. The network targets the 15–39 demographic specialises in a chart-music playlist of pop, rock, hip hop and dance music. It reaches approximately 486,800 listeners weekly, making it the fifth largest commercial radio station in New Zealand. The ZM network as it is today was founded in the early 1970s as three separate commercial music stations owned by Radio New Zealand in Auckland, Wellington and Christchurch. The name is derived from the former callsigns of the stations: 1ZM, 2ZM and 3ZM. The stations were carved off to The Radio Network (now merged into New Zealand Media and Entertainment) in 1996, and ZM spread across the country, originally as three separate networks before finally merging to form one nationwide network in 2000. The network's head office and main studios are based in Auckland, where all of the programming is produced. ZM history Early years ZM in its current format was first started in 1973 by the government owned New Zealand Broadcasting Corporation (which became Radio New Zealand in 1975). The three original ZM stations were based in Auckland, Wellington and Christchurch and had been on air for the past few decades most recently as 1YD, 2YD and 3ZM in their respective markets. The three original stations were known by their ZM call signs, 1ZM in Auckland on 1250AM, 2ZM in Wellington on 1130AM and 3ZM in Christchurch on 1400AM. In 1978 the AM frequency step in New Zealand was changed from a 10 kHz step to a 9 kHz step as a result all three stations changed frequencies. 1ZM moved to 1251 kHz, 2ZM Wellington moved to 1161 kHz but sometimes branded as 1162ZM and 3ZM Christchurch moved to 1323 kHz. 1980s Overnight programming In 1981, Radio New Zealand stations were finally granted the right to broadcast 24 hours per day; previously only the domain of private operators. Overnight networked programming was introduced with the ZM All-Nighter show. Programming was produced from the 1ZM studios in Auckland and networked to 2ZM Wellington and 3ZM Christchurch. 2ZK in Hawkes Bay and 4ZG in Gore also took the ZM All-Nighter. Programming was also networked to the ZMFM station introduced in Palmerston North in 1987. The show was offered as an