Systems and methods that can externally meter and display cumulative, noncumulative, and re-settable service hours for monitored equipment as well as provide data associated with incremental amounts of equipment usage. The sound-energy of the left and right input signals is separated and corrected in a first low-frequency range and a second high-frequency range. The end caps have outer surfaces. In an arrangement, energy values in the wedge region of the scalogram may be estimated by calculating a set of estimation locations in the wedge region and estimating scalogram energy values at each location.