<prompt> The Most convenient form of a cross cylinder is a combination of0.5 Diopter sphere with 1 Diopter Cylinder0.5 Diopter sphere with 1 Diopter Cylinder0.25 Diopter sphere with 0.5 Diopter Cylinder0.25 Diopter sphere with 0.5 Diopter Cylinder  <response>: The most convenient form is a combination of a -0.5D sphere with a 1.0D cylinder which has an effective strength of 0.5D cylinder in one meridian and -0.5D in other. 