GAP is the minimum gap in time between the previous stop time and the current scan start time when scheduling with DURation or DWELL. For scheduling with DURation, it will be that time interval. For scheduling with DWELL, the interval might be longer if required for slews, but it will not be shorter. Note that both PRESCAN and MINPAUSE are applied after the scan times are established and a negative PRESCAN could make the period during which the tape is stopped shorter than GAP. MINPAUSE is used to keep the tapes rolling through short gaps. Note that, if START is specified, GAP will be ignored.
If LST scheduling, GAP is a sidereal time, so it will be slightly shorter in UT (by about 1.0027).
For all types of scheduling, if the gap between scans is less than 10 seconds, the tapes are left running.
The current status of PCFS software requires an interval of 36 seconds at tape reversals to produce a valid VEX file. A 40 second gap is required to change setup. Apart from these restrictions continuous recording is implied for gaps shorter than 10 seconds. In addition, users should realize that during continuous tape motion no calibration data is taken. Starting and stopping the recording can be forced using GAP or PRESCAN, or by using START times. GAP is probably the prefered mechanism.