DOVEX tells SCHED to write a VEX format output file. It is now the default so the parameter can be used to turn off writing of the VEX file. VEX is the format originally used by PCFS, the NASA/Goddard field system that controls EVN, geodetic and other stations. It is now used to control most correlators including the VLBA and other DifX correlators, the JIVE correlator and the geodetic correlators based on the Haystack design. VEX files will also eventually be used for control of the VLBA stations and the EVLA for VLBI. So a VEX file is required for essentially all VLBI observations now.