Actually, for LevelFit the precision of the setting angles
('delta_angle') should be taken into account. DT, DO and DC,
the absolute errors in reciprocal space in reciprocal Å, are given
by:
-
DT =
(2/) *
,
DO =
(2/) *
sin *
,
DC =
(2/) *
sin *
B,
with all delta's in radians and
=
B *
cosB,
(Subscript B for 'Bisecting'). The corresponding vectors, DT, DO and DC,
form a "monoclinic cell" with unique angle (90+) between DT and DO.
The maximal combined error D is given by:
-
D = (DT*DT + DO*DO + DC*DC + 2*DO*DT*sin),
from D = DT - DO + DC, the longest body diagonal of the "cell".
Example: for Mo-radiation ( = 0.71Å), = 15° and errors
of 0.01° in and ,
and 0.03 in B we have (if we are not
mistaken): DT = 1/2034, DO = 1/7859, DC = 1/2620 and therefore D = 1/1514
reciprocal Å, so 1/1000 is a good choice here. (We prefer writing
1/1514 to 0.000660501 because this is easier to visualize, and to
emphasise the reciprocal nature of the magnitudes.)