System and method to detect battery cell malfunctions through redundant offset battery cell monitoring. In exemplary embodiments, neural or neuromuscular activity is analyzed to determine a focus or other quality of a visual input, and this focus or quality information used as a basis for controlling an adjustable lens system. The approach is applicable to a wide variety of contexts and is ideally suited for automatically selecting rental items to be recommended for rental. The loop includes a first portion that is moved at a continuous speed relative to the support structure, and a second portion that is alternatively moved and stopped relative to the support structure. The information about the performance of the pump may include information about pump performance monitoring by a slip flow measurement, about predicting impeller wear, about pump impeller cavitation monitoring, about pump monitoring through acoustic emissions, about pump leak detection, about pump efficiency monitoring and about positive displacement pump monitoring. In one embodiment, the OFDM communications system includes an OFDM transmitter that generates a training sequence that includes a fractional tone in a guard band thereof and transmits the training sequence via a channel.