Logical pair monitoring that accounts for the grey zone

We develop the approach of logical pairwise monitoring for functional units of various nature with simultaneous monitoring of both the main (functional) and control (monitoring) parts of the system. We introduce the definition of a grey zone for pair monitoring caused by the limited capabilities of the functional unit needed for monitoring the separation of parts that implement its purpose and carry out built-in monitoring. We study the manifestations of these limitations and propose a methodology for the practical use of logical pairwise monitoring that takes into account their presence. We give an illustrative example.