The instrument should then be set at zero or “plano,” a position indicated by the appearance of the three “0 0 0” at the spherical register, in conjunction with one “0” or zero, for the cylinder at its register, marked “CC Cyl.” After this move, the supplementary disk’s pointer should be set at “open” (Fig. 2). [Illustration: Fig. 3—To obtain sphericals, turn this Single Reel as shown by dotted finger. This assures an automatic and simultaneous registration at sphere indicator of focus of lens appearing at sight opening.] CONVEX SPHERICAL LENSES A careful study will show that the Ski-optometer’s spherical lenses are obtained by merely turning the smaller reel (Fig. 3). The first _outward_ turn of this reel, toward the temporal side of the instrument, draws into position in regular order the spherical lenses +.25, +.50, +.75, and +1.D., as shown in Fig. 3a. [Illustration: 3-A—Outer spherical reel containing Cx. sphericals from .025 to 1.00D and a blank.] [Illustration: 3-B—Inner spherical disk containing Cx. sphericals, automatically turns within 3-A.] [Illustration: 3-C—Supplementary spherical disk.] By means of a concealed tooth gear, an inner disk is automatically picked up, placing its first lens +1.25D in position (Fig. 3b). This +1.25D spherical lens remains stationary while the outer disk again revolves, adding to it the original +.25, +.50, +.75 and +1.D., the latter totalling +2.25D. At this point, the instrument again automatically picks up its inner disk, thereby placing its second lens, +2.50D, in position. [Illustration: Fig. 4—With the reappearance of “00” at sphere indicator, a rapid increase or decrease of +1.25 is accurately and speedily attained.] Instead of using intermediate strengths in making an examination, it is frequently desirable to make such extended changes as 1.25D to 2.50D. With the Ski-optometer, the refractionist will note that two white zeros appeared at the spherical register in connection with +1.25, and again with +2.50. A rapid outward turn of the spherical reel toward the temporal side to the point of the reappearance of the two zeros will show +3.75D; or, if increased power is still desired, a rapid turn will draw +5.D. into position (Fig. 4). Turning the reel inward toward the nasal side will likewise decrease its convex power. In brief, each one of these lenses, showing their foci in conjunction with the two white zeros, are signals indicating the rapid increase or decrease of one and one-quarter diopter. After continuing to +6D., the next turn automatically shows zero (or “plano”), the original starting point, which is again indicated by the three white zeros. Through the turn of the single reel—an exclusive Ski-optometer feature—all convex spherical lenses have now been attained in quarters up to +6.D, practically covering ninety percent of all refraction cases.