In a complete rotation, spindle of a screw gauge advances by 12mm. There are 50 divisions on circular scale. The main scale has 12 mm marks → (is graduated to 12mm or has least count = 12 mm or has least count = 12 mm) If a wire is put between the jaws, 3 main scale divisions are clearly visible, and 20 division of circular scale co-inside with the reference line. Find diameter of wire in correct S.F.