Bill Watterson took two sabbaticals from writing Calvin and Hobbes: the first from May 6th, 1991 to February 1st, 1992, and the second from April 4th through December 31, 1994. At the end of the first sabbatical, Watterson changed the rearrangeable Sunday strip format to the unbreakable 1/2 page design. The concept of 9-month sabbaticals was novel at the time, and began to be recognized by other comic strip artists afterwards. As such, Watterson effectively popularized the concept of sabbaticals.