HEADMODE. This allows the user to set the head usage mode. Such a mode includes the head positions for each pass and the sequence of head positions to use for passes. There are two options and a default. Use of anything except the default (blank) is only recommended for system tests. The first option is VLBA14 which is the standard VLBA/MARKIV sequence with 14 head positions. The other option is MKIV2H which is appropriate for Mark IV wide band observations that use two headstacks. If MKIV2H is set by the user, or more likely by the program when in TWOHEAD mode, NEADHDPOS is forced to 6.