The measure of absolute structure (enantiomorph or polarity) as
defined by Rogers.
The value must lie in the 99.97% Gaussian confidence interval
-1 -3u =< \h =< 1 + 3u and a standard uncertainty (estimated
standard deviation) u must be supplied. The item range of
[-1.0, 1.0] is correctly interpreted as meaning
(-1.0 - 3u) =< \h =< (1.0 + 3u).
Ref: Rogers, D. (1981). Acta Cryst. A37, 734-741.