The Tektronix 155-0009-00 (M001) is a Tek-made horizontal lockout logic chip in a 16-pin DIP, designed by Les Larson.
It receives inputs from the horizontal chop and alt. binary, "A" sweep delay control, "A" sweep gate, "B" sweep holdoff and "B" sweep gate. Logic is performed on these signals to provide lockout for "A" sweep or "B" sweep and alternating signals for the horizontal chop and alt. binary.