[evlatests] Source position offsets versus distance from calibrator

[Eric Greisen]

Barry Clark wrote:
> I think what Ed is saying is that the frequency used to calculate
> u,v is wrong by 375 kHz.  Might this be related to the half channel
> labeling error in AIPS that people were muttering about the other
> day?
> 

I believe that the conclusion from that previous discussion was that the 
data appear to be at a frequency 1/2 channel different than the 
frequency which was commanded in the observation and which casa and aips 
  subsequently reported.

Perhaps this all boils down to understanding what the commanded 
frequency means.  Michael stated that it is the low end of the first 
channel and that is what casa and aips then see - an integer at the low 
end of the channel.  If instead some other software in the correlator 
setup takes that commanded frequency to be the center of the first 
channel, then the data would differ from the labels.

AIPS will allow one to test Barry's hypothesis...

Eric