                   Notes on the NUMBER OF CHANNELS
                        in Version 2 Specpr

     Version 2 specpr supports a number of channels value that ranges
between 1 and 4852.  You should be sure that the correct number of
channels are set BEFORE completing ANY MATH OPERATION.

RULES of Operation:

     The math routines use the number of channels set by the wavelength
set to determine what to operate on.  For example if you have two 512
point spectra, and the wavelengths are set to 81 channels, then any
math (e.g. divide) will only work on 81 channels.  There are some
execptions (f14: edit, it will work on all 4852 channels).  If you have
any doubt, set the number of channels BEFORE entering the routine, or
if it gives you the option, when you first enter it.  All routines
that operate on certain number of channels inform you of how many
channels it will use.

     When a math operation is complete, the program goes to the CRT plot
routines.  The NUMBER OF CHANNELS RECORDED IN THE HEADER to the data
is set after you exit the plot routines and uses the number of channels
given by the wavelength set in use.  For example, consider you had just
divided two spectra of 512 channels.  When you exit the CRT plot routines
and the data are written, the number of channels are set by the wavelength
set currently in use.  If you changed the wavelength set in the CRT plot
routines to 22 channels, when you exit the plot the program sets the
channels to 22, copies 22 channels to the output I/O buffer and
writes the results to disk and you didn't get all your data.  So, be
careful.  Most routines that have different output channels from
input channels will automatically set the output to the correct
values (e.g., f17: convolution).

IF YOU MUST CHANGE THE NUMBER OF CHANNELS:

   MATH: CHANGE the WAVELENGTH SET number of channels.  DO NOT go
to the header information change routines and change the value there:
it gets overwritten by the value from the wavelength set when the data
are written to disk (after you exit the CRT plot routines).

   DISPLAY: Change protection on the data file to -1.  Then transfer the
data to itself.  For example, if the data you wanted to change was in
v23 and had a length of 512 channels and you really wanted 510, then
you would set the protection on v to -1, and from transfer routines,
use the command "v23citv23" (see section 10), then change the number
of channels value and exit the information change routines using "e"
(exit and do pending write of the data back to disk).  BE CAREFUL: if
you change the channels to a bigger number, there is really no data in
those new channels.  ALSO, if you increase the number of channels too much,
you will go over a record boundary and the next record could be written
over other data!  If you use a much smaller number, the output data
could take up less records and then there would be a record that had
its continuation bit turned on, but has no beginning data to it.  A
list of the data file will cause a read error at that record.  In that
case, you need to write a dummy data set in that record.  To do that,
copy (transfer) a data set whose number of channels is less than or 
equal to 256 to that record.  BE SURE  and RESET protection to the end
of the file so you do not overwrite other data!

SETTING CHANNELS:

    Sometimes you must set the number of channels to a value that you
do not have a wavelength set for.  Use the capital c "C" and a number.
For example, you have just started specpr in a new directory and have
no data in any file.  You can not display something because you have
nothing to display.  Go to MATH and operate on something that doesn't
need input data.  For example, do f16 (line segment generator).  When
you enter f16, set the number of channels to whatever you want and type 
in some values (e.g. set channel 1 to 0 and channel 2 to 0 and exit to
the CRT plot).  You can then write that data as a dummy data set.
Many specpr users usually start every data file with a dummy data set
where the title has the name of the data file (archive tape name) and
maybe a description of the project.
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