A general question about PID Controller

I have a basic question because I'm trying to understand right now a concept that I thought it was obvious. Looking at this video he is going to feedback the variable state x with the input of the system, which is a force f.

Now, if I'm correct it is only possibile to feedback variables which share the same units, so I expect to drive a meter through an input variable which is a meter and the difference will be then feed into the PID. Is the example in the video just to show up how to use simulink? Or I m wrong?

\begin{align} e &= x - x^d \\ u_f &= -k_p e - k_d \dot{e} \end{align} If $x$ and $e$ have units of [m] and $u_f$ needs to have units of [N], then we get $k_p$ with units of [N/m] and $k_d$ with units of [N/(m/s)]