A New Model of BAM: Alpha-Beta Bidirectional Associative Memories.

A shade of adjustable width is provided in which portions can be removed by tearing along score lines, and means including pull tabs are provided whereby a portion in the margin of the shade may be removed leaving a widened opening which terminates at an apex at a given score line such that pulling adjacent portions of the shade material concentrates stress at the score line and promotes clean tearing therealong.