A power miter saw includes an activation assembly including a lever, a spring loaded drive rod passing through an underside of the table, a curved link pivotably secured to the drive rod, a pivotal member pivotably secured to the curved link and secured to the lever, a driven rod, a clamping member in an edge of a positioning seat, and an axle through the positioning seat and having an end pivotably disposed in a support seat; a graduated member including apertures; and a locking device including a hollow member having two side slots, a spring loaded cam member, and a transverse bar passing through the positioning seat, the slots, and the cam member; a spring loaded pin secured to a forward end of the hollow member; and two lever members secured to two ends of the transverse bar respectively. A pivotal movement of the lever unfastens a positioning seat.