ROUTINE “A” ROUTINE “B” (Made with _minus_ cylinder) (Made with _plus_ cylinder) Sph. +1.D. Cyl. Axis Sph. +1.D. Cyl. Axis Step 1 +1.D. = -.25 ax. 180° equal to +.75 = +.25 ax. 90° Step 2 +1.D. = -.50 ax. 180° equal to +.50 = +.50 ax. 90° Step 3 +1.D. = -.75 ax. 180° equal to +.25 = +.75 ax. 90° Step 4 +1.D. = -1 ax. 180° equal to 0 +1 ax. 90° In brief the method of using minus cylinders exclusively in an examination, as explained in routine “A”, necessitates the change of the cylinder lenses only after the _strongest_ plus sphere is secured. On the other hand, notwithstanding innumerable other methods where plus cylinders are used, routine “B” shows that the best spherical lens strength the patient will accept, is also first determined. Then both spheres and cylinders are changed in their regular order by gradually building up in routine, by increasing plus cylinder and next decreasing sphere, a quarter diopter each time, until the final result is secured. While it is conceded that both routine “A” and “B” are of themselves simplified methods, by comparing routine “A” where minus cylinders are used with routine “B” where plus cylinders are used in their corresponding steps, the refractionist will note by comparison that one is the exact equivalent and transposition of the other. Where _plus_ cylinders are employed, eight lens changes are made before final results are secured; while but four lens changes are necessary where _minus_ cylinders are used. The refractionist should also note by comparison that the use of minus cylinders reduces focus of the plus sphere, but only in the meridian of the axis. It has not made the patient myopic. Furthermore, a plus cylinder will bring the focal rays forward, while minus cylinders throw them backward toward the retina. This is but another reason for the exclusive use of minus cylinders in refraction. The method of using _minus cylinders_ exclusively in an examination, necessitates the change of the cylinder lenses _only_. On the other hand, the method of using plus cylinders makes it necessary to change spheres and cylinders in routine. In brief, since using the minus cylinder is merely a matter of mathematical optics, their use even in a trial-case examination is strongly urged. The maximum value of the Ski-optometer is fully realized only when the advantages of using minus cylinders exclusively in every examination is clearly understood. CONSTANT ATTENTION NOT REQUIRED With the Ski-optometer, when the examination is completed, the sum-total of final results—whether spherical, cylinder, axis, or all combined—are automatically indicated or registered ready to write the prescription. _Until then_, the foci of the various lenses that may be employed are of no importance.