How to calculate the coefficient of restitution?

The coefficient of restitution often denoted ${\displaystyle e}$ can be found with some notion of Newton's Experimental Law.
This law states that: ""in a system of colliding bodies(usually 2 bodies) the relative velocity of separation is directly proportional to the relative velocity of approach"".
Mathematically expressed, ${\displaystyle V_A-V_B\alpha U_A-U_B}$
${\displaystyle \text{or}{V}_B-V_A\alpha U_B-U_A}$
For a system of colliding bodies ${\displaystyle \text{A}}$ and ${\displaystyle \text{B}}$
The constant of proportionality is ${\displaystyle -e}$
Thus we have,
${\displaystyle V_A-V_B=-e(U_A-U_B)}$
${\displaystyle \Rightarrow e=-\frac{V_A-V_B}{U_A-U_B}}$
The initial and final velocities of the two bodies colliding are all that are required to calculate e.