ad - Make a weighted average of additional scans with those
	in stack2 (if any)					RWW & MWP

ad 80a108_112,bbe:	Add scans 108 to 112 from file c80a into stack 2. Use
			The 1 Mhz filter bank. Scans which are not the same
			type as 108 will not be added.
ad a9993_b4,mh:		Look through scans 80a9993 to 80b4 and add the ones
			which are the same type as 80a9993 and match header
			values with stack 2. If stack 2 is empty, the matches
			are made with 9993.
em;ad 108_112,cr:1	Average together the scans which match 108 in the group
			108 to 112 and keep moderately bad data.

ad 108_112 ss:3		Average together all #3 subscans in the scans 108 to 
		        112. (for more info on subscans, see 'gt ?!')

For a scan number, or a range of scan numbers using the step size, each
scan is read. All of the scans which pass a series of tests are
averaged into stack 2 (see co for details of this process).At the end,
stack 2 is copied into stack 1.  If some scans were not used, the
number is printed.  A flag is set to show that stack 1 has not been
plotted.  This will trigger a plot at the end of the command line it
the auto plot option is on.  The scan number range may span more than
one file.

Step size may be either positive or negative as long as it is
appropriate for the range of scan numbers given.

The observation type (fs,ps,cal, etc.) of the first scan is saved and
succeeding scans are used only if they have the same type.  If a scan
has been marked bad by setting ndat(34) to a positive value, the scan
is rejected if ncare+ndat(3) is greater than 2. If the matching header
flag is set, the header values freq, position, filter width,amt of freq
switch, and lsr velocity are checked against stack 2, and if any are
different, the scan is rejected.

If the matching header flag is not set, the header values are still
checked for a match. If differences are found, you will be asked
whether you wish to proceed. If you answer yes, all further mismatches
of the same type will be ignored, but if other mismatches occur, you
will be questioned again. If your answer is no, the command will be
aborted, stack 1 will contain the offending scan, and stack 2 will
contain all of the scans added so far.

You may specify the backend to be used either by number or type.
Continuum scans are processed without using the backend parameter.

The current 'scan number' is shared with gt.

See the gt documentation for a discussion of the special rules for
typing scan numbers in comb.

This document was last updated on Tue Oct 17 16:24:05 EDT 2000 by Marc W. Pound.