Helpful Hints Clean lenses as well as possible with alcohol or lens cleaner. Frame temples must be in the open position as not to obscure the light filter. Switch on power. Two (2) high intensity fluorescent tubes will light in a few seconds. Position the lens, with the front surface facing you, between the light source and the magnifying lens; holding the lens approximately  7.0 - 8.0 cm. from the light source initially, move the lens nearer or further from the magnifying lens to achieve optimum image resolution. The operators eyes should be approximately  20 cm. away from the magnifying lens.   Glass and Plastic Lenses High minus, badly scratched or dark sunglass lenses can be more easily found when removed from the frame. Angling the lenses slightly may ease observing very faint markings, particularly those on high minus lenses. Anti-reflection coated lenses may have had their engravings etched away in preparation to coating. In some instances the nasal engraving may have been ground away, in the case of very narrow  P.D. It is beneficial to be familiar with the general location of the engravings, see diagram. A few brands of PAL's are not engraved, see OLA lens guide®.   Glass Lenses    (Require Nr.2 Light Filter) Thoroughly remove all fingerprints and oils from the surface of the lens. Glass engravings are finer than those in plastic lenses, and require a bit more practice by the operator. The engraved area in positioned along the edge of the black central disk, not directly above the perimeter light. The light source should only indirectly illuminate the engraving, with the marking contrasted above the blacked out area of the filter.