The time period of a simple pendulum is given by $T = 2\pi\sqrt{\frac{l}{g}} + kx$, where $l$ is the length, $g$ is acceleration due to gravity, and $x$ is displacement. The dimensions of $k$ are:

One is equivalent to 931 MeV energy. The rest mass of electron is $9.1 imes {10^{ - 31}}kg$. the Mass equivalent energy is (1 amu = $= 1.67 imes {10^{ - 17}}kg$)