According to the principle of his work, LeWitt's wall drawings are usually executed by people other than the artist himself. Even after his death, people are still making these drawings.[19] He would therefore eventually use teams of assistants to create such works. Writing about making wall drawings, LeWitt himself observed in 1971 that "each person draws a line differently and each person understands words differently".[20] Between 1968 and his death in 2007, LeWitt created more than 1,270 wall drawings.[21] The wall drawings, executed on-site, generally exist for the duration of an exhibition; they are then destroyed, giving the work in its physical form an ephemeral quality.[22] They can be installed, removed, and then reinstalled in another location, as many times as required for exhibition purposes. When transferred to another location, the number of walls can change only by ensuring that the proportions of the original diagram are retained.[23]