Originally self-released as a reel to reel stereo tape in 1970 in an edition of only 10 copies. Ostensibly, it's one long sublime drone that can be played in either channel or both, forwards or backwards, at any speed you like and for as long as you like. It's well worth nipping across to the release page for a broader explanation.
Double CD released on Important Records in 2009.
Vice Versa, etc....