The ″Inners″ apporach is introduced and utilized to develop a criterion that determines the capability of a linear model to approximate a physical system. The technique essentially involves the determination of the class of physical systems which includes the particular mechanism of interest, the quantification of system characteristics of linear models in this class using the roots of associated transfer functions, the development of a region in the complex plane which encompasses these roots, and the utilization of Inners method using a computer algorithm to determine whether the model of the system of interest has its roots within the region. The merit of this approach is that it is an immediate and inexpensive means of determining the accuracy of a model prior to extensive simulation of a possible faulty model. The particular class of systems of interest here are the neuromuscular control mechanisms. Models of muscle, versional and vergence eye tracking, accommodation, the pupil light reflex, the semicircular canals, the vestibular system and the hand are discussed.