1. A method of correcting an error in the measurement of a process variable taken sensor in a chemical process system characterized by properties which causes at least some of the measurements to be erroneous, the method comprising the steps of: identifying the component of the error caused by dynamic state factors, this component of the error being determined by at least once obtaining a senor measurement in the system and noting how that measurement deviates from an objectively correct measurement of the process variable by varying amounts relative to time, identifying the steady state factor component of the error, this component of the error being determined by at least once obtaining a senor measurements and noting that the measurement deviates from the objectively correct measurement of the process variable by a fixed amount relative to time, identifying the component of the error caused by additional factors, and altering the measurement to remove the errors caused by steady state factors, dynamic state factors, and unknown factors.