From: Helmut Coelfen <coelfen@castor.mpikg-teltow.mpg.de>
  To  : rasmb@bbri.harvard.edu
  Date: Thu, 10 Apr 97 15:44:04 +0200

Binary files

Dear RASMB,
Tom Laue suggested in his last contribution to take out the radial positions 
from
the absorbance scans and to replace them by informations which allow to
reconstruct the radial positions lateron in order to make the file more compact.
This is in principle a good idea but I question if it works for absorption
scans. The problem with at least my machine is that the interval between
two radii stored in the XL-A file is not always equal to the interval which has
been selected in the software. E.g. I can input a radial step size of 0.001 cm
but the actual intervals in the ASCII output files are often larger. This is due
to the precision of the radial scanning system of only 0.005 cm. The same
holds for wavelength scans. Here, the precision is only 4 nm. Regardless
if I select a 1 nm step size or not, I end up with steps in the wavelengths 
of up 
to 4 nm. Therefore, it will be not possible to restore the radial data by giving
the number of data points and the limiting radial values of the scan for
example. For obvious reasons, mistakes will occur if the corresponding
absorbance - radius values are restored. The only way round this I see
at the moment is to read out the radial step size as well which then will
allow a correct restore of the radius. However, all step sizes are almost 
as many numbers as radial values and hence this is not practical. Maybe
an interval storage of the kind 5 * 0.001, 1 * 0.002, 9 * 0.001 etc. could lead
to a data reduction as fortunately, most radial step sizes are equal to
what the user has selected. Whatever one does, I just want to point out
that the solution of this problem is not straightforward.

Another point Tom made and which sounds reasonable to me is to
leave ASCII as the default outpt of the AUC software and give
a binary output option for those who can take advantage of them.
This would be a compromise probably satisfying most of us.

Best wishes

Helmut Coelfen

P.S. Is there any reference to the approach of Yphantis and Lary storing
more than one scan in a file so that one can get more familiar with that
approach and how it works precisely ?