Which of the following statement is incorrect?

Which of the following technique is not used for measuring small time intervals?

The relative errors in the measurement of two lengths 1.02 cm $$\pm$$ 0.01 cm and 9.89 cm $$\pm$$ 0.01 cm is

Suppose refractive index $$\alpha$$ is given as $$ \alpha = A + {B \over {{\lambda ^2}}}$$, where A and B are constants and $$\lambda$$ is wavelength, then dimensions of B are same as that of