Ralf;

This is my objection, just because his Yv >c does not mean his v >c. c= x/t or x'/t'. That is c's invariance and max velocity from any perspective. I use Yc or Yv = x/t'. No odometer required, I'm assuming space is invariant. I'm also not violating the formula for c. The ship travelling 4ly to proxima Centauri according to his starcharts from the earth perspective at .8c will do that trip in Yv= 5/3 * 4/5 = 4/3c but that is x/t' not x/t. He's using his own clock readings to measure his Yv. He has not violated c because from his perspective c travels at Yc = 5/3 c. Light will still beat him to his destination. Using Yv and distance travelled in his own time has no need for an odometer because space need not be warped.

[Speed does not vary. The anaut Biff can measure his speed relative to earth as he leaves, and his speed relative to the target as he approaches. Per the earth frame E (left), his arrival event A is E(x, t) = E(4, 5). SR allows Biff to assume a pseudo rest frame (right), so the arrival event A' is (0, 3). Biff will always measure light speed as c (2nd postulate). His clock is slow and so is his biological clock, thus he is not aware of any time discrepancy. The left compares Biff's perception of his motion to that of E. He thinks he is closer to E because less time has elapsed on his clock. Note, he still has the same speed.

coordinate transformations from E to Biff:

x'=5/3(x-vt) = 5/3(0) = 0,

t'=5/3(t-vx) = 5/3(1. 8) = 3,

in agreement with the graphic.]