23. A method as recited in claim 22 additionally comprising the step of determining a sign for the difference between the first and third signals.
23. A method as recited in claim 22 additionally comprising the step of determining a sign for the difference between the first and third signals. 24. A method as recited in claim 23 wherein the first and second sensed linguistic variables and associated function sets correspond to the guidance point error signal and rate of change error signal respectively and each has a fixed plurality of members corresponding to different values of the corresponding sensed linguistic variables, each of said members being programmable to vary a classification of a given value of a sensed variable signal.