Antibiotic Zone Reader is used for determining the strength of antibiotic material. It functions by measuring the diameter from 0 to 80.0 mm of an inhibition zone in a petri-dish. Wells are created on a petri-dish, prepared with agar solution and inoculated with bacteria. After incubation, the bacterial growth cover the dish except for a circular inhibited zone around each disc, it being a function of the strength of the antibiotic. The zone reader accurately measures the diameter of the inhibited zone to 0.1 mm within range of 0 to 80.0 mm diameter. Light is passed through the transparent and semitransparent portions of the agar from a source at base towards up. It then passed to a reflecting mirror supported by an arm above the unit, which reflects the light to glass prism mounted at the front of the unit and magnified image of the zone of inhibition is clearly visible on the prism.