I am currently trying to understand SR and am confused on this postulate. Lets say somone is traveling on a some kind of machine that emits photons. When that photon is emited will the person traveling on the machine measure the photon going c or will they measure it going c-v? My next question is will an outside observer view the photon as going c or c+v? I'm guessing that the person on the machine will measure it as c-v and the stationary observer will measure it as c but I am not sure.