$$\require{cancel}$$
Suppose that you have deduced (or have read in a book) that the period of oscillations of a torsion pendulum is $$P = 2 \pi \sqrt{\frac{I}{C}}$$, where $$I$$ is the rotational inertia and $$c$$ is the torsion constant. You have to check to see whether the dimensions of the right hand side are indeed that of time. We have
$\left[\sqrt{\frac{I}{C}}\right] = \sqrt{\frac{\text{ML}^2}{\text{ML}^2 \text{T}^{-2}}}.$
This does indeed come to $$T$$, and so the equation balances dimensionally.