The diameter of a wire is measured with a screw gauge having 50 divisions on circular scale and by one complete rotation of circular scale, main scale moves $0.5 \mathrm{~mm}$. If reading of screw gauge is $0.250 \mathrm{~cm}$. The minimum percentage error in the reading will be
(A) $0.4$
(B) $0.8$
(C) 4
(D) 5