A few specific scenarios applied in examples of only five works suggest
that the solely use of robust estimators for nonlinear dynamic data
reconciliation is able to cope with biased measurements. We present a
counterexample to that belief on a dynamic model of two CSTRs that gives
rise to wrong transient behaviour. Motivated by this, we introduce and
examine an invariant approach to measurement bias. It is based on the
location invariance assured by a robust measure of scale used when
detecting a sequence of consecutive differences between measured and
reconciled values of the same sign. When applied to the counterexample,
it can be seen that the procedure has the correct behaviour and shows
good results.