Syntax: CURSOR
or      CURSOR WORD1 WORD2

   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. You should not use <CR>, as it is often used by
the cursor hardware.

   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.