What is this data cutoff?

Jian-Ping Xiong xiong at acpub.duke.edu
Thu Sep 25 00:33:24 EST 1997

I am working on two data sets using X-plor: one from crystal with heavy
the other from crystal without heavy atom. Refinement works great for
from crystal without heavy atom, but something strange happens for data
crystal with heavy atom in refinement(SA or positional) step:

 	After asymmetric reduction, resolution, F and sigma cutoff, another
selection (cutoff) was executed on the reflection data before the
refinement started. This selection cut out another about 35% of reduced
reflections,i.e. only about 65% of reduced reflections were used in the
consequent refinement.

What is this selection?  Any instruction or hint?

Many thanks for your attention.

Jian-Ping Xiong

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