Methods and apparatus, including computer program products, implementing and using techniques for coordinating grid tracking and character composition. T-shaped tabs are disposed at an upper end of the upstanding edge regions, whereby the collecting tank has a flange rear engageable at least in part by the T-shaped tabs. The blades can be locked in place by the cam lock which is attached to the foot plate by means of a screw and foot pocket by means of an adjustable pull lanyard. A shield is fixed on one of the chassis and the cover. In one embodiment a switch is switched on for an on time period that is substantially fixed in response to the slope of the voltage across the switch while the switch is off.