1. A computer-implemented method for monitoring and diagnosing anomalies in auxiliary systems of a gas turbine, the method implemented using a system having a processor, a user interface, and a memory, the method comprising: storing a plurality of rule sets in the memory being relative to the auxiliary systems of the gas turbine, the plurality of rule sets comprising at least one rule expressed as a relational expression of a real-time data output relative to a real-time data input, the relational expression being specific to at least one of process parameters associated with the auxiliary systems of the gas turbine; receiving real-time and historical data inputs from a condition monitoring system associated with the gas turbine, the real-time and historical data inputs relating to a value of at least one of the process parameters associated with the auxiliary systems of the gas turbine; and estimating values for at least one of the process parameters associated with the auxiliary systems of the gas turbine based on the received real-time and historical data inputs and at least one rule of the plurality of rule sets.