The prior variances supplied, together with any observations over D, must be coherent. The COHERENCE: command can be used to perform coherence checking for variance matrices to be used in an adjustment. Otherwise, whenever an adjustment is calculated, [B/D] checks for the coherence of the variance specifications required for any analysis, and also checks that the data, if any, are consistent with the variance matrix specified over D, in the following context.
Suppose that the data quantities 
for an adjustment are observed
to be 
. These data are inconsistent with the beliefs specified
beforehand if, for any linear combination 
, we have
and 
(that is, we
observed a change in a quantity whose value we believed we knew with
certainty). The datawarn and
datawarn+ options are used to set the level of detail output
when data inconsistency is detected, and the datawarn
control can be set to warn about data inconsistency, rather than
flagging it as an error. When flagged as an error, the default, the
calculation of the adjustment fails. Otherwise, the adjustment proceeds
as normal but of course the status of the results involving the data
will be unclear.