Its's really just a matter of consistent usage of units in the math. The Photon doesn't care how we define it's movements/existence.
Luckily for us, the base SI unit for length (m) is defined in terms of the distance light travels in some unit time (1/299,792,458 seconds)
https://en.wikipedia.org/wiki/Metre
https://en.wikipedia.org/wiki/Second
https://en.wikipedia.org/wiki/Speed_of_light
HPC Engineer with a strong penchant for physics
I've worked with a lot of eccentric professor types... maybe its rubbed off on me..