Which of the following is most accurate?

Options

1. AA screw gauge of least count $0.001 \mathrm{ mm}$.
2. BA screw gauge having pitch $1 \mathrm{ mm}$ and 50 divisions on circular scale.
3. CA vernier callipers of least count $0.01 \mathrm{ mm}$.
4. DVernier callipers having 20 divisions on the sliding scale (vernier scale) coinciding 19 divisions on the main millimetre scale.