Digital antibiotic zone reader determines strength of antibiotic materials by measuring diameters from 0 to 80.0 mm of inhibited zones in petri dishes. Agar in petri dish is inoculated with bacteria, and then sensitivity dishes are dispensed onto dish. After incubation , bacterial growth covers dish except for circular inhibited zone around each disc. Zone diameter is a fiction of antibiotic strengh. Light from base passes up through transparent &semitransparent portions of agar. Adjustable rubber belt sliding , facilitates positioning of dish relative to light source. Light then passes Technical Specification Digital Display 4 digit (9999 max). Dish Size 110mmdia. Magnification 100 mm. / Standard Accessaries - Marking pen, Magnifier Lense Holder. to reflecting mirror which reflects image, on glass prism with horizontal line mark on it. Arc from one edge of circle zone is adjusted tangent with line on viewing glass by the “slider knob”. Now hold the left side knob & turn the right side dial & adjust zero.Then entire dish is to be moved by turning “slider knob” until are from opposite side of inhibited zone is brought tangentto same line. Take down the reading from the dial.