### 6 Internal Data Areas

There are seven internal data areas into which data may be read. These are as follows:

XCOL
– This area is principally intended to hold X-axis data. However, when using the command PLOTHIST H, this area is intended to hold the data before they are binned to draw the histogram.

When using the command ERRORBAR X with the symmetric option turned off, this area contains the position of one of the ends of the error bar.

YCOL
– This area is intended to hold Y-axis data.

When using the command ERRORBAR Y with the symmetric option turned off, this area contains the position of one of the ends of the error bar.

EXCOL
– This area is principally intended to hold errors for the X-axis data values. These errors are generally assumed to be symmetric about the data point by the command ERRORBAR, but with the symmetric option turned off EXCOL holds the position of the opposite end of the error bar to XCOL.

The EXCOL area is assumed to contain the standard error of the XCOL data by the command ELLIPSES.

The EXCOL area is also used to hold the X-axis component of the vector offset from the data point by the command VECT, and the proper motion in Right Ascension by the command PVECT.

When using the command ARC, the EXCOL data are assumed to contain the magnitude of the semi-major axis of the ellipse.

The command AVEDAT will write the standard deviation of the average it calculated for each bin into the EXCOL data area.

EYCOL
– Similar to EXCOL, but applying to the Y-axis data values.

The EYCOL area is used to hold the Y-axis component of the vector offset from the data point by the command VECT, and the proper motion in Declination by the command PVECT.

When using the command ARC, the EYCOL data are assumed to contain the magnitude of the semi-minor axis of the ellipse.

ZCOL
– PONGO does not have the ability to draw three dimensional plots. As a result, the ZCOL data area does not contain Z-axis data in the conventional sense. However, there are a number of commands that use the values stored in the ZCOL area.

The command SIZEPLOT uses the values stored in ZCOL to scale the size of the marker symbols plotted for each data point.

The commands VECT and PVECT can optionally use the values in ZCOL to scale the length of the vectors they draw.

The command ELLIPSES assumes that ZCOL contains the values of the normalised covariances between the X- and Y-axis errors.

LABCOL
This area is used for storing a character string associated with each of the data points. The strings may be plotted interactively using the ANNOTATE or CURSE commands.
SYMCOL
This area is used to store a PGPLOT symbol number (an INTEGER) associated with each of the data points.