A.a -0.50D sphere is coupled with a -1.00D cylinder
B.is useful in refining the spherical power during trial of lens
C.the handle is mounted parallel to one of the axis of the cylinders
D.when refining the power of a trial cylinder，the handle of the Jackson cross-cylinder is placed in line with the axis of the trial cylinder
E.a Jackson cross-cylinder designated 1.00D consists of a +1.00D cylinder