An electric power tool includes a housing, an inner case and a hammer case. As long as a number of preconditions are met, such as vehicle speed within speed range, fueling command above a fueling threshold, gear ratio within a predefined range and VA above an acceleration threshold, the control circuit computes a number of instantaneous vehicle mass estimates as a function of the VA and FDW values. The aperture is formed from portions of the refractive body surrounding the lens and can act to divert excess light from the optical path of the scanner by refraction or reflection. The strap tightening device is engaged with a step formed in the front end of the seat bottom to hold the seat bottom securely on the seat of a vehicle by the straps. The normalized data is then fit to simulated data that is associated with a model having an untextured substrate and one or more variable parameters.