Telescope Jumps: One Cause is Found . ... One tries to take out the sag of the secondary cage as the telescope is pointed toward the zenith. The second component tries to take out changes in the secondary piston caused by temperature changes of the truss structure. ... Second, the jumps only occur when the temperature data causes motions of the piston which go in a direction opposite to the direction in which the sag component is driving the secondary. ... One has to wonder how this can occur. ...