The mean ratio of absolute anomalous intensity
differences to their standard deviation within the
spherical shell (defined by its diffraction limits
_reflns_shell.d_resolution_high and
_reflns_shell.d_resolution_low).
|Dano|
-------------
sigma(Dano)
with
Dano = I(+) - I(-)
sigma(Dano) = sqrt( sigma(I(+))2 + sigma(I(-))2 )