Patent ID: 7333919

Claim:
A method of detecting perturbation of a physical system from a reference state associated with a reference parameter (ω 0 ) to a perturbed state associated with a perturbed parameter (ω), the method including the steps of: a) deriving the reference parameter (ω 0 ); b) deriving a reference entity (F) which describes the system's state at the reference parameter (ω 0 ); c) deriving an error entity (E) from the difference between the reference entity (F) and a measurement-related entity (Z) associated with a perturbed state of the system; and d) using the error entity (E) to provide an indication of whether or not the system state has been perturbed from the state associated with the reference parameter (ω 0 ), with the perturbed parameter (ω) having become unequal to the reference parameter (ω 0 ).