QDP reads the ASCII file containing various plotting commands and the data,
then calls the PLT subroutines which then executes the commands and plot the
data. At this point the `PLT>` prompt appears and the user can then proceed to
perform the following:

- Display information about the interactive commands via HElp.
- Override various PLT defaults.
- Override the default PLT commands
- Add/remove labels.
- Plot data with various combinations of lines, markers, and error bars.
- Change the appearance/style of the of the plot, for example converting all text into Roman Font.
- Plot the data as a function of a different x variable.
- Change the number of panels in which the data is plotted.
- Define models and to calculate the 'best fit' parameter values.
- Generate hardcopy.

QDP/PLT can be run interactively within each XRONOS application by
entering commands at the `PLT>` prompt, or can automatically
execute commands from a script with the hidden parameter
`plotfile`.

A few, commonly used QDP/PLT commands are given below; the full descriptions of
the PLT commands are in the "QDP/PLT User's Guide" or can be listed on the
terminal by typing `?` or `help` from the PLT prompt.

Rescaling: to rescale X and Y axes use:

PLT> r x xlow xhigh PLT> r y ylow yhigh PLT> r xlow xhigh ylow yhighLogarithmic Axes: to make the x and/or y axes logarithmic (to the base 10) use:

PLT> log x PLT> log yTo turn off the logarithmic axes use

PLT> log offDevice: to change the current plot device use:

PLT> dev /xxxwhere

Modelling and Fitting: to use the fitting capability of QDP/PLT two are the
main commands `MOdel` and `FIT`. The `MOdel` command is used to define the
model, any combination of model components can be added together.
For example:

PLT> mo cons linr quadwill add a constant, a linear and a quadratic term. The list of the available models is given typing:

PLT> mo ?The

Replot: after making changes in the PLT environment, a replot will show the effects of the modifications

PLT> p

Hardcopy: a hardcopy of the current plot is obtained using:

PLT> hardcopy filenameThe file is in postscript.

EXit: to exit from the PLT subroutine type:

PLT> exitQDP was written and is currently maintained by Allyn Tennant, at the Marshall Space Flight Center. PGPLOT, provided and maintained by Tim Pearson, is the graphics package used by QDP/PLT.

For programs that handle simultaneously more than one time series (*e.g.*
lcurve and efold) different types of analysis result can be plotted
depending on the number of input time series. For two input time
series, three different plots are provided (1) the sum of the
intensities of the two input series on the X-axis and on the Y-axis the
count ratio (ser2/ser1) of the two input series (Hardness-plot); (2)
Time (or Phase) on the X-axis and the intensity on the Y-axis for the
two input time series; (3) As (2) but also the ratio is plotted. For
three or four input time series two different plots are available: (1)
Colour-Colour diagram that shows the ratio of ser3/ser2 or ser4/ser3 on
the Y-axis (for 3 or 4 input series respectively) and ser2/ser1
(always) on the X-axis; (2) Time (or Phase) on the X-axis and the
intensity on the Y-axis for the 3 (or 4) input time series.

The choice of the plot type is done by setting the parameter
`plotdnum`. Note that in the `efold` plot with Phase on the X-axis, the
Y-axis can be either count/s or count/s normalised by average source
intensity. Note that for the multicolor tasks all the arrays
calculated by lcurve or efold are available in `PLT>`. A color ratio
plot versus time or phase can be obtained as follows. At the prompt:

Two plotting styles available: Colour-Colour [1] ; Intensity vs Time (or Phase)[ # of series (3 or 4)]; Enter PLOT style number (default=1)[]Enter the number of time series. On the screen the plot has as many panels as many input series, showing the counts for each series on the Y-axis and time or phase on the X-axis.At the

PLT> info Scales: Grp Wind Label XData Min XData Max YData Min YData Max 1 -1 Time (s) : 3496. , 8646. : 3496. , 8646. 2 2 Ser 1 : 3496. , 8646. : 331.8 , 466.4 3 3 Ser 2 : 3496. , 8646. : 415.9 , 613.8 4 4 Ser 3 : 3496. , 8646. : 747.7 , 1080. 5 -1 Ser 2/Ser : 3496. , 8646. : 1.222 , 1.325 6 -1 Ser 3/Ser : 3496. , 8646. : 1.755 , 1.819 7 -1 Ser 1+2+3 : 3496. , 8646. : 1495. , 2160. 8 -1 : 3496. , 8646. : 1.000 , 1.000 PLT>To plot the ratios (array number 5 and 6) versus time together with the three input lightcurves use the following commands:

PLT> color 1 on 5 6 PLT> plot ver PLT> plotThe final plot will contain 5 panels. The first three are the input series the last two the ratios.