[dleviwing]

Hi Jon D;
I’m not sure what you are attempting to state but, Va is a constant, so I don’t understand the need to produce another constant P unless you wish to reference all motion values to that P quantitative value. This would be a mathematical normalization such to say P=1/c. I guess this would be OK to determine the derivatives but it is not needed at this level of the discussion.

In most physics equations, Va would be equal to 2c
In quantum physics however, it would be equal to the expansion value of the universe. You can select either value unless you get into theoretical quantum processes.

Can I assume you have had calculus? If so, it might be better to express P as a derivative of Va to produce the normalization.