Since the beginning of this series we've established that the foundation of the relationship between mechanics and kinematics is the connection between pairs of mechanical quantities and kinematic power laws. This relationship can be conveniently expressed as a link between a variable length and a variable time. Nevertheless, we've seen in episode 7 that other kinematic perspectives are equally legitimate: velocity profiles where a speed is given versus a length, dispersion relations where a frequency is given from a wavenumber, or even more exotic pairing as was the case for turbulent spectra. The perspective is a matter of choice. However, in this 8th episode on mechanics, we will see that for a given pair of mechanical parameters, there exists a privileged perspective depending on a single variable in direct relation to the mechanical ratio. This special kinematic variable provides what we can call the "right angle" on the dynamics. How to construct this perspective and what is gained from it is what we will try to find out.  We will see how for each regime we can identify a "constant variable", a combination of compensating variables, constant in the range of validity of the regime. When this constant variable is properly scaled by the mechanical ratio it is what has come to be called a dimensionless number. These dimensionless numbers initiate a far reaching reflection on the relationship between numbers and units, and provide a way to represent kinematics with objective rather than subjective units.