The defaults plot settings are the following:`
SET MODE TIME
SET X TIME
SET Y AMPLITUDE PHASE /LIMITS 0 * -180 180
SET ASPECT_RATIO 2.0 AUTO
SET SUBBANDS C01 TO C06
SET BANDS LOWER
SET BASELINES 12 13 23 14 24 34
SET AVERAGING NONE
SET PHASES DEGREES JUMPY
SET PLOT POINTS`

Thus the `PLOT` command will produce six plots in six GREG boxes; one
for amplitude versus time and one for phase versus time, for the three
baselines linking the three first antennas. The data plotted will be the
average of the 6 continuum channels (C01 to C06) for the upper side band.
No time averaging will be done (one point plotted for each data point
recorded), the phase will be in degrees with no 360 degrees jumps.

The `SET X` and `SET Y` commands are needed to choose the
variables to be plotted. In time-like mode the variables may be the
components of the visibilities (amplitude, phase, real part or imaginary
part), or the baselines coordinates `U`, `V`, `RADIUS` or ` ANGLE` (the rectangular or polar coordinates of the baseline vector in
the plane perpendicular to the source direction). Other variables are time
(in hours of Universal Time), scan number, source direction
(`HOUR_ANGLE`

and `DECLINATION`), or delays (see the internal help
or section 8 for a complete description).

The `SET BANDS` command will select the side bands plotted. Several
side bands may be plotted simultaneously. Side bands may obviously be ` UPPER` or `LOWER`, or `AVERAGE`, where the weighted average of
both side bands will be used to compute the components of the visibilities
if any are to be plotted, or `RATIO`, in which case the (unweighted)
ratio USB/LSB will be used. The weights for averaging the side bands are
entered by the `SET AVERAGING` command.

The `SET SUBBANDS` command is used to specify the sub-bands to be
used. Sub-bands are referred to by their mnemonics `C01`, ..., ` C06`, for the continuum sub-bands, `L01`, ..., `L06` for the
line sub-bands. In CLIC, L01 refers to the first available line subband,
L02 to the second one, and so on. They correspond to the bands selected in
the `SPECTRAL` command in OBS. Several continuum sub-bands may be
averaged together by specifying a range (e.g. `C01 TO C05`, or `C01
AND C04`, or `C01 AND C03 TO C06`, the latter just excluding ` C02`).

For line sub-bands all the channels are averaged together, except if the
`/WINDOW` option is used. For instance:
`SET SUBBAND L01 /WINDOW
30 45`

will average visibilities in channels 30 to 45 of the first line
sub-band. However the edge channels (with lower signal-to-noise ratio,
due to anti-aliasing filters in the correlators) may be left out, by using
e.g. `SET DROP 0.1` to leave out of the bandwidth at each edge
of each spectral subband (the default is only ). The central
channels, possibly affected by the Gibbs phenomenon in case of scontinuum
signal in the image subband, are left out by using command
`SET GIBBS` `number`, `number` is the number of channels left
out

The `SET BASELINES` command obviously selects the baselines for which
data is to be plotted. Baselines are named 12, 13, 23, (14, 24, 34,
...). Note that the numbers here refers the ordinal numbers of the
antennas that where connected at the time of the observations. If only two
antennas were connected, only one baseline will be in the data, and it will
be referred to as ``12'', even though the antennas you used are labelled
``2'' and ``3'' in black paint, and were at this time connected to
correlator inputs ``1'' and ``3''! However this hardware information is
recorded in the header, for possible needs.

A `SET ANTENNA` command is also available. It is used to plot
antenna-related parameters (such as `TSYS`, Elevation, ...) or with
autocorrelation data (`SET Y AUTO`). It may also be used (in time-like
mode only) with correlation data: in that case,

- amplitude for each antenna is computed from ratios of baseline
amplitudes in the following
way:

(averaged over possible antennas j and k, different of i and of each other). This actually is a measurement of the gain of antenna i, if a point source is observed. It is a convenient way of displaying pointing and focussing data, but three antennas at least are needed. - antenna phases are computed by using the closure relations (the phases of all antennas are computed by a least square fit, assuming that antenna 1 has a phase of zero).

The `SET AVERAGING` command deals with the way data is averaged. Data
may be time-averaged by the `PLOT` command; `SET AVERAGING TIME t`
will specify the averaging time, while `SET AVERAGING SCAN` will force
averaging observation by observation, and `SET AVERAGING NONE` will
turn off time averaging. The normal method is to average complex
visibilities (`SET AVERAGING METHOD VECTOR`, the default), while an
alternate method is to average separately amplitude and phases (`SET
AVERAGING METHOD SCALAR`).

Side band averaging, and sub-band averaging are always done in vector
method. The weights for side band averaging are specified by the commands
`SET AVERAGING UPPER baseline amplitude phase` and `SET AVERAGING
LOWER baseline amplitude phase`. These weights should be determined from
the data, using plots of both amplitude and phase of the side band ratios.

The plotting may be done either with GREG symbols (`SET PLOT POINTS`,
the default), or with lines connecting the points (`SET PLOT LINES`),
with histograms (`SET PLOT HISTOGRAM`), or with error bars (in the case
of visibilities only; type `SET PLOT BARS`).

Finally the command `SET ASPECT_RATIO`
selects a default x/y aspect ratio in the cases when several boxes will be
plotted. The boxes will be positioned on the screen to approach this ratio
as much as possible (`SET ASPECT_RATIO value AUTO`), or will exactly
reflect the demanded aspect ratio (`SET ASPECT_RATIO value EXACT`).

After a plot has been obtained, coordinates of special points may be
obtained interactively by command `CURSOR`, which calls the interactive
graphic cursor. Striking almost any key will give the user coordinates of
the cursor, while ``E'' is used as usual to exit the cursor mode; ``K''
will delete the selected data point from the current plot (useful to avoid
this point in `SOLVE PHASE`); you may also `IGNORE` or `TAG`
scans in a given range to a given quality: type N to open a new range, and
`I` or `T` to close it (if using `T` you will be prompted for
the quality in the range 0-9). Finally ``F'' may be used in the same manner
as ``T'' to interactively flag bad data points in the data (see section
4.6.2)

After the `PLOT` command, the abscissae and ordinates of the plotted
data points are kept in two two-dimensional SIC arrays named `X_DATA`
and `Y_DATA`, where the first index is the data point counter (1 to
`N_DATA`) and the second index is the box number. Thus the data are
available for more specific plots or mathematical operations using the
possibilities of SIC and GREG.