An apparatus and method is provided for removing undesired twists and loops in a power supply cable attached to a robotic swimming pool cleaner during the cleaner’s pre-programmed movement over the bottom andor side walls of the pool. The ultrasonic transducer includes a resonator composed of ceramic material and positioned between a head mass and the piezoelectric crystal. The airbag is disposed in the case so that the wound body is deployed upward or downward while rolling along a front surface of the legs so as to be unwound when being inflated. A cachability measure for the link may be determined based on whether a plurality of previous requests for the link returned the other content object, an annotation in a link map, a probability of traversing the link, a network metric, or the like. The stray light may be monitored, and if a threshold level of stray light is reached or exceeded, the use of the exposure tool may be discontinued for a particular type of semiconductor product, resist, or mask level, until the lens system is cleaned.