A screw gauge has 100 divisions on the circular scale and linear distance travelled by the head scale is 5 mm in 10 complete rotation of circular scale. When nothing is placed between its studs, the zero of circular scale is 26 divisions above the reference line, it means zero error is $-26$ divisions on the circular scale. Now if the diameter of a wire is measured by keeping the wire between its studs, the main scale reading is 6 divisions and 48th division of circular scale coincides with the reference line. If the negative zero error of screw gauge is x mm and the measured diameter of the wire is y mm.