How do we determine relativistic velocity if velocity is a function of distance and time and if distance and time in Special Relativity are both functions of velocity? From the point of an outside observer, if velocity increases then time dilates. Due to the inversely proportional relation to velocity, a slower time would result in a higher velocity. Therefore would a constant acceleration not actually be a constant acceleration relative to the outside observer? V = ∆x / t where t = to * sqrt( 1 - [v/c]2)-1 Where V equals the previous equation, etc.