I think that you are looking for A.J.C. Wilson, Acta Cryst. 17 (1964)
1591-2.
George
Prof. George M. Sheldrick FRS
Dept. Structural Chemistry,
University of Goettingen,
Tammannstr. 4,
D37077 Goettingen, Germany
Tel. +49-551-39-3021 or -3068
Fax. +49-551-39-22582
On Wed, 17 Sep 2008, Ian Tickle
All - I've been trying to track down a paper (or papers) where it was
shown that the epsilon values (symmetry factors) for space groups with
pure rotation axes are not integers as is usually assumed (but still
integers for screw axes). It's almost certainly in Acta Cryst.,
probably in the 60's or
