Suppose there is a starting point A from which your ship is moving away from. At the same time, a photon is shot out from A. You can take the distance traversed between A and the ship as D1, and the distance traversed by the photon as D2. Then your "percentage of C" is D1/D2.
How can you get the distance D2? I'm not sure. I guess we have to pretend it's also a ship that is traveling at C that can emit information to us (also at C :p )
Suppose there is a starting point A from which your ship is moving away from. At the same time, a photon is shot out from A. You can take the distance traversed between A and the ship as D1, and the distance traversed by the photon as D2. Then your "percentage of C" is D1/D2.
How can you get the distance D2? I'm not sure. I guess we have to pretend it's also a ship that is traveling at C that can emit information to us (also at C :p )