... Triggers the use of multiple phase center processing on the DiFX correlator at least at the VLBA. In practice, this puts the list of phase centers in the .v2d file used in setting up correlation. ... The argument of CENTERS must correspond to a list of names in the phase center groups listed after a PCENTERS command. For now, there is no clear way to make the phase center list scan dependent, so specify the same name for each scan on the same source. ... Usage: Keeps value of previous scan. ...