The first part of the set is a one-off performance of a musical play retrospectively entitled Progress?, and featuring members of the BBC Symphony Orchestra. Portions of this performance originally found their way on to the second Mystery Disc (released in 1986 as part of the box set The Old Masters Box Two and issued as an individual album in 1998) and the Honker Home Video release of Uncle Meat (1989). Much of the humour and storyline of the play is lost to the casual listener due to primitive recording techniques and the visual nature of some of the performance, necessitating extensive liner notes by Zappa.
According to Zappa's liner notes, the remainder of the set is "A fair – not outstanding – 1968 Mothers of Invention rock concert performance". Different edits of snatches from the second part of the performance ("The Orange County Lumber Truck" and "Prelude to the Afternoon of a Sexually Aroused Gas Mask") were originally released on Weasels Ripped My Flesh (1970).
