An audio signal is sampled and a frequency transform is performed on a succession of sets of samples of the signal to obtain a time dependent power spectrum for the audio signal. The optical conversion elements comprise light-receiving areas configured in a pattern which corresponds to the pattern of the test plate. The regulating knob includes a tube portion, a front end of which is formed into steps gradually lowered in a circumferential direction, and hollow projections spaced along an inner wall surface corresponding to the steps for engaging with the steel ball on the connector to locate the regulating knob in place. Projected timelines for completion, tracking of materials used and materials stored, and partial payments and releases are all managed by the system based on inputs by participating parties.