A student measured the diameter of a small steel ball using a screw gauge of least count 0.001 cm. The main scale reading is 5 mm and zero of circular scale division coincides with 25 divisions above the reference level. If screw gauge has a zero error of –0.004 cm, the correct diameter of the ball is : 

0.529 cm 

MSR = 0.5 cm ; CSR = 25 x 0.001 cm ; Zero Error = - 0.004 cm

Total Reading = MSR + CSR - Zero Error = 0.5 cm + 0.025 cm - 0.004 cm = 0.529 cm