Radial Velocity of the centre of mass of spectroscopic binary system

[JordanGo]

My book says (Foundations of Astrophysics):
" The radial velocity ... can be found from the Doppler shift of the star's absorption lines:
$\nu_{r}=\frac{\Delta\lambda}{\lambda}c$
If the star you are observing is part of a spectroscopic binary system, you can separate the radial velocity of the star relative to the center of mass and the radial velocity of the center of mass itself. This can be done by averaging the radial velocity of the star over an entire period."

Now I am confused how to find the radial velocity of the center of mass. Can someone show me how?

 

[Nate810]

The radial velocity of the center of mass can be found by averaging the radial velocity of the star over a period. This can be done by taking the mean of the observed radial velocities of the star at different points in its orbit. For example, if you were to observe the star at 4 different points in its orbit, you would calculate the mean of those 4 radial velocity values and that would give you the average radial velocity of the center of mass.