[,<src>[,<src>]] sets the source of the parameter to be measured.   
  When <item> is PERiod, FREQuency, PWIDth, NWIDth, PDUTy, NDUTy, RDELay, 
FDELay, RPHase, or FPHase, the range of <src> is 
{D0|D1|D2|D3|D4|D5|D6|D7|D8|D9|D10|D11|D12|D13|D14|D15|CHANnel1|CHAN
nel2|CHANnel3|CHANnel4|MATH}. 
When <item> is any of other measurement parameters, the range of <src> is 
{CHANnel1|CHANnel2|CHANnel3|CHANnel4|MATH}. 
  If the parameter to be measured only needs a single source (VMAX, VMIN, VPP, 
VTOP, VBASe, VAMP, VAVG, VRMS, OVERshoot, MARea, MPARea, PREShoot, PERiod, 
FREQuency, RTIMe, FTIMe, PWIDth, NWIDth, PDUTy, NDUTy, TVMAX, TVMIN, 
PSLEWrate, NSLEWrate, VUPper, VMID, VLOWer, VARIance, PVRMS, PPULses, 
NPULses, PEDGes, and NEDGes), you only need to set a single source. If 
[,<src>[,<src>]] is omitted, the source is the one selected by the :MEASure:SOURce 
command by default.   
  If the parameter to be measured needs two sources (RDELay, FDELay, RPHase, and 
FPHase), the command needs to include two sources; otherwise, the command is 
invalid. If [,<src>[,<src>]] is omitted, the sources are the ones selected by 
the :MEASure:SETup:DSA and :MEASure:SETup:DSB or :MEASure:SETup:PSA 
and :MEASure:SETup:PSB commands by default.