In an experiment of measuring the refractive index of a glass slab using travelling microscope in physics lab, a student measures real thickness of…

In an experiment of measuring the refractive index of a glass slab using travelling microscope in physics lab, a student measures real thickness of the glass slab as $\displaystyle 5.25$ mm and apparent thickness of the glass slab as $\displaystyle 5.00$ mm . Travelling microscope has $\displaystyle 20$ divisions in one cm on main scale and $\displaystyle 50$ divisions on vernier scale is equal to $\displaystyle 49$ divisions on main scale. The estimated uncertainty in the measurement of refractive index of the slab is $\displaystyle \frac{x}{10} \times 10^{-3}$, where $\displaystyle x$ is $\displaystyle \_\_\_\_$