Abstract: A lock apparatus operable by combination or key includes a cylinder plug secured at a reference orientation relative to a frame by a plurality of detent wafers biased for engagement with a primary keyway in the frame, and a combination dial mounted coaxially about the cylinder plug and operably connected to the detent wafers by a plurality of cam rings mounted about the frame and cylinder plug for engaging a plurality of associated radial push pins arranged to force the detent wafers out of the primary keyway. The detent wafers are removed from engagement with the keyway by insertion of a key within the cylinder plug or by entry of a combination using the dial to allow rotation of the cylinder plug and an output nut carried thereby away from the cylinder plug's reference orientation. A ratchet-driven cam tube is provided for automatically scrambling the cam rings during operation of the lock apparatus.