In a vernier callipers, there are 10 divisions on the vernier scale and 1 cm on the main scale is divided in 10 parts. While measuring a length, the zero of the vernier lies just ahead of 1.8 cm mark and 4th division of vernier coincides with a main scale division.
(a) Find the length.
(b) If zero error of vernier callipers is - 0.02 cm, what is the correct length ?