Background: John William Carson (October 23, 1925 - January 23, 2005) was an American television host, comedian, writer, and producer. He is best known as the host of The Tonight Show Starring Johnny Carson (1962-1992). Carson received six Emmy Awards, the Television Academy's 1980 Governor's Award, and a 1985 Peabody Award. He was inducted into the Television Academy Hall of Fame in 1987.
Context: On May 1, 1972, the show was moved from Thirty Rockefeller Plaza, New York, to Burbank, California, because of the studio's proximity to the celebrities. Carson often joked about "beautiful downtown Burbank" and referred to "beautiful downtown Bakersfield", which prompted Bakersfield Mayor Mary K. Shell to chide Carson and invite him to her city to see improvements made during the early 1980s.  From July 1971, Carson stopped hosting five shows per week. Instead, Mondays featured a guest host, leaving Carson to host the other four weeknights. Shows were videotaped in Burbank at 5:30 pm, fed from there to the Central and Eastern time zone stations via cross-country television line at 8:30 pm Pacific time (11:30 pm Eastern time), and later sent from Burbank to the Pacific time zone stations at 11:30 pm Pacific time. Since only two feeds originated from Burbank, Central time zone stations received the Eastern feed one hour earlier at 10:30 pm local time, and Mountain time stations received the Pacific time zone feed one hour later at 12:30 am local time.  In 1980, at Carson's request, the show cut its 90-minute format to 60 minutes on September 16; Tom Snyder's Tomorrow added a half-hour to fill the vacant time. Joan Rivers became the "permanent" guest host from September 1983 until 1986. The Tonight Show returned to using rotating guest hosts, including comic George Carlin. Jay Leno then became the exclusive guest host in fall 1987. Leno joked that although other guest hosts had upped their fees, he had kept his low, assuring himself more bookings. Eventually, Monday night was for Leno, Tuesday for The Best of Carson--rebroadcasts usually dating from a year earlier, but occasionally from the 1970s.  Although Carson's work schedule became more attenuated, Tonight remained so successful that his compensation from NBC continued to rise; by the mid-1970s, he had become the highest-paid personality on television, earning about $4 million a year ($15,008,000 today), not including nightclub appearances and his other businesses. He refused many offers to appear in films, including title roles in The Thomas Crown Affair and Gene Wilder's role in Blazing Saddles. He also declined director Martin Scorsese's offer to co-star with Robert De Niro in the 1983 film The King of Comedy, the role of a TV talk-show host then going to Jerry Lewis.  In recognition of his 25th anniversary on The Tonight Show, Carson received a personal Peabody Award, the board saying he had "become an American institution, a household word, [and] the most widely quoted American." They also said they "felt the time had come to recognize the contributions that Johnny has made to television, to humor, and to America."
Question: How often was his show on?. Whats the answer?