Tektronix 2247A Operator's Manual page 71

Operators Familiarization
If DELAY Is selected, the C/T is used to measure the time Intervals, as
explained above for ALT horlzontal mode (except that no Intensified
zones are displayed in B horizontal mode). The k- OR DELAY control
knob positions both delay times (reference and delta) together, and
the -4 control knob positions the Independent delta delay.
Message Reason
NO A SWEEP No A sweep was detected after timeout
{ALT or B Horizontal MODE).
2247A Operators 3-19