The following observations were taken for determining surface tension of water by capillary tube method:
Diameter of capillary $\mathrm{D}=1.25\times {10}^{-2}\mathrm{m}$ and rise of water in capillary $\mathrm{h}=1.45\times {10}^{-2}\mathrm{m}.$
Taking $\mathrm{g}=9.80{\mathrm{ms}}^{-2}$ and using the relation $\mathrm{T}=\frac{\mathrm{rgh}}{2}\times {10}^3{\mathrm{Nm}}^{-1},$ what is the possible error in surface tension $\mathrm{T}$?

For a post office Box, the graph of galvanometer deflection versus $R$ (resistance pulled out of $RB$ ) for the ratio $100: 1$ is given as shown. A careless student pulls out two non consecutive values $\mathrm{R}$ marked in the graph. Find the value of unknown resistance.

Consider a home made vernier scale as shown in the figure. In this diagram, we are interested in measuring the length of the line $PQ$. If both the inclines are identical and their angles are equal to $\theta$ then what is the least count of the instrument.