CHECK that you are not trying to display something that is not being
generated, e.g., the 2nd frequency when you have a correlator configuration
for only one bandpass, or cross products when they are not being
generated.
If any antennas are not ``on source'' (e.g., because an antenna was
detached or behind the others due to a recent stop), then
if VIS is in onsource mode, it will only display visibilities if
all antennas are on source. Onsource mode is convenient
as one doesn't want to see the visibilities while antennas are slewing.
If you want to retain onsource mode, however get it to ignore
a detached antenna type in VIS:
For e.g.,
array 12456
This will plot all except antenna 3
baselines.
(Onsource mode can be toggled on and off, onsource).
If the visibilities are absent or completely flat,
ensure that a suitable set of display buffers, called variables, has
been defined. Do this on the SPD terminal.
array 12456