A portable saw has a depth or blade lowering control and an adjustable stop for selecting the maximum depth of the blade to which the blade can be lowered. According to one exemplary embodiment, the head restraint assembly is configured for use with a vehicle seat having a collapsible seat back for providing improved clearance as the seat back moves between a use position and a storage position. The sensor initialization protocol may include applying a first series of voltage pulses to the sensor. And the invention has a few parts, and can set it the state where the driver bit chosen by easy operation can be used, and the storage state easily. A preferred transmission path is autonomously determined at each of the autonomous telemetry stations.