The Selectable Trigger System allows the operator to choose between two different modes of actuation with the twist of a switch. 1) Sequential Trip Actuation: This mode requires the operator to hold the tool onto the work surface before pulling the trigger. This makes accurate fastener placement easier. It allows exact fastener location without the possibility of driving a second fastener on recoil. 2) Contact Trip Actuation: This mode allows the operator to contact the work surface to actuate the trip mechanism while keeping the trigger pulled, thus driving a fastener each time the work suface is contacted. This will allow rapid fastener placement. SX1838K owners should carefully read the Tool Operation and Trip Operation Modes section of the Operation and Maintenance Manual before operating this tool.