[Illustration: Fig. 12—(A. and B.)—This unique, patented split-spring device of screwless construction, securely holds all movable parts. In case of repair, they may be removed with the blade of a knife.] The Ski-optometer is built on the plan of ¹/₁₀₀₀″, insuring absolute rigidity and accuracy and a lifetime of endurance. Particular and detailed attention has been given to the novel means of eliminating screws which either bind, create friction or continually work loose, causing false indications of findings on scales of measurements; hence correct and accurate indications are insured in the Ski-optometer by means of a split-spring washer construction similar to that of an automobile tire’s detachable rim (Fig. 12). This patented spring washer construction securely holds the phorometer lenses, the rotary prism and the revolving cylinder lens cells. Whenever necessary, or in case of repair, these parts may be readily removed with the blade of a knife. CHAPTER V CONDENSED PROCEDURE FOR MAKING SPHERE AND CYLINDER TEST WITH THE SKI-OPTOMETER Notwithstanding various methods employed, for both subjective and objective refraction, the following synopsis of the previous chapters will unquestionably prove most valuable to the busy refractionist, enabling him to make error-proof examinations in practically every case without resorting to the transference of trial-case sphere or cylinder lenses. A careful reading of chapters one and two should be made however, so that one may gain an understanding as to how spheres and cylinders are obtained with the Ski-optometer. SUBJECTIVE DISTANCE TEST 1st—Place Ski-optometer in position, employing spirit level, thus maintaining instrument’s horizontal balance. 2nd—Adjust the pupillary distance for each eye individually, by drawing an imaginary vertical line downward through the center of each eye from the 90° point on the Ski-optometer’s axis scale. The opaque disk should be placed before the patient’s left eye by setting the supplementary disk handle at “shut.” 3rd—The Ski-optometer lens battery before the patient’s right eye should be set at “open” (figure 2), whereupon the first turn of spherical lens battery toward the nasal side places a +6.D sphere in position. This should blur vision of average patient. 4th—It is now only necessary to remember that an outward turn toward temporal side of the instrument increases plus sphere power, while a nasal turn decreases it. Therefore continue to reduce convex spherical lens power until the large letter “E” on the distant test card is clear. Then request patient to read as far down as possible,—a rapid turn of a quarter diopter being readily accomplished with the Ski-optometer (Fig. 4).