Syntax: CURSOR
or      CURSOR WORD1 WORD2
or      CURSOR READ

   Display the crosshair cursor to enable you to get positions (in
user coordinates).  Positions are typed on the screen following
(almost) any key (followed by a newline if the key was a digit; you
get a number of positions).  Exit the cursor routine by hitting the
'e' or 'q' key. If you exit with 'e', CURSOR issues a relocate command
to set the current plot position to the cursor position, and this
command is entered onto the history buffer. With a 'q' exit, no
command is entered (but the position is still updated).  You should
not use <CR>, as it is often used by the cursor hardware.

   You can simply read the current cursor position using CURSOR READ.

   The second form defines a pair of vectors WORD1 and WORD2 from the
position of the cursor when an `e', 'm', or `p' is hit, use `q' to
exit without marking the current cursor position (`m' doesn't print
the current cursor position). ^C aborts the command with no vectors
defined. Note that to use SPLINE on the resulting vector, the x
coordinates must be monotonic increasing, but see also the SORT
command.

   Use IMAGE CURSOR if you want to get the value of an image as well
as the cursor position.
