Current top performing SAPI systems are B4C-containing. The systems incorporate real-time phase, amplitude and frequency analysis of a subject’s electro-encephalogram. The housing encloses an interior space of the wireless field device. The linear dynamometer is then used to measure a force profile applied by the body portion over a predefined range of motion at a predefined linear velocity. The method continues by, when the determined response compares unfavorably with the desired response, determining a response offset based on a difference between the determined response and the desired response. The aminobiguanides are useful in the preservation of pharmaceutical compositions, particularly ophthalmic pharmaceutical compositions and compositions for treating contact lenses.