I assume in an SR example of a propagating sphere of light from a pinhead size event that its propagation symetry is independent of the frame which created it. The point on the frame which created the event must be somewhere within the sphere. Use three photons on the sphere to create a target. 1. Any one photon 2. A photon heading out on the reciprocal of the first photon. 3. A photon heading out at 90 degrees to the line formed by the first two photons. During propagation of the three photons take a small target of some mass and hold it on the reciprocal of the three photons for a short duration and release. The target will now be inertial and remain on the reciprocal of the three photons. Is it reasonable to suggest the photons move at c from the point marked by the target to the edge of the sphere but not at c from the point on the frame they left unless that point remains with the target. Are these reasonable assumptions or at what specific point am I mistaken. I find this can be used as the basis for simple SR calculations.