A method for analyzing a photomask comprises the determination of a Bossung plot. The position of the steering column is adjustable when the lever is in the unlocked position and fixed when the lever is in the locked position. The mode transition is signaled by transmitting a known transition sequence on the monitor tones over two or more successive symbol intervals while simultaneously transmitting data on at least some of the tones in the range other than the monitor tones. Data about an event detected at a first sensor is compared with events detected at other sensors in order to identify correlated events from which connections between the sensor locations can be inferred and a building layout generated.