# Units of Klein-Gordon equation

I'm looking at the units of the Klein-Gordon equation $$u_{tt} - c^2\Delta u = -\frac{m^2c^2}{\hbar^2}u.$$ Disregarding the units of $$u$$, which are the same everywhere and so cancel, I get $$seconds^{-2}$$ for both terms on the LHS, but $$meters^{-2}$$ on the RHS. What am I doing wrong?

You are missing a $$c^2$$ on the RHS, equation should be
$$\color{red}{\frac{1}{c^2}}u_{tt} - \Delta u = -\frac{m^2 c^2}{\hbar^2}u$$
$$u_{tt} - c^2\Delta u = -\frac{m^2 \color{red}{c^4}}{\hbar^2}u$$