15.60.1  POINTS 

     READ POINTS [APPEND=ON|OFF]] [SET]

This reads in data to be plotted.  Once data is read, it is retained until
it  has  been used to generate a plot.  It is then discarded when new data
is read.  Normally you plot the data immediately after reading  it.   When
you  start  a  new  plot,  the  data  last  plotted is still available for 
replotting.  It is not discarded until  new  data  is  read.   The  option
APPEND  allows  you  to append more data to the already plotted data.  The
option SET starts a new data set.  If you do not  specify  a  symbol  when
reading points, the default is determined by the last SET SYMBOL command.

This  command  is not necessary, since TOPDRAWER assumes that a number not
preceded by a command is automatically a point.  If you wish to read  data
with the symbol as the first item, you must use the READ DATA command, and
terminate the data with a blank line.

Values that are omitted are initially set to 0.0, or to the previous value
for that field.

When reading in data <XVALUE>, <DXVALUE>, <YVALUE>, ...  are the X, DX, Y,
...  values from the previous point.