When I say Va - Vb = Vab this is the relative velicity of the A a]nd B system; Va' - Vb = Va'b is the relative veloity of the A' anb B system for which we seek a zero final answer which allows us to reduce the total relative velocity number to arrive at the result at ehich time the contribution of the A frame velocity to the total relative velocity,which is simply the defintioin of absolte veocity of the isidvidual system frame components. Do not bristle at "absolte velocity", nor take offence at "contributed velocity" as these terms are both anehema to the postulated structure of SR. Yuriy, I cannot consiider for any reason that you could t understanad completely the significance of an inertial system having its relative motion expressed in terms of the measured velocity of the individiual sysrtem inertial components such as the A and B absolute velocities. Velocitiies with respect to what you may ask? The answer: Velocity With respect to the inertial component trajectories them selves, not with respect to each other. This would put us back into the SR hole we just climbed out of. There is no such thing as absolute velocity zero? Prove it using something else than by SR which by this time is simply toast, There may technnological obstructions of locating the trajectory track or coordinate line but that is an engneering problem one that would be enormously pleasurable and satisfying to solve.Any attempt to demand some abstract or even real point on theoretical bases is to leap recklessly and irresponsibly int the abyss of an inite regression that could only be averted by the insertion of erzats and arbitrary mathematical contrivances]. To adopt the trajectory of the frame is to adopt a straight line through space until acted upon by an external force. What else do you need for an inertial frqame, thisn isn the se]f definition of an inertial frame, If there are any objections based on a incosistences assiged in the Galilean structure vis a viks naxwell's equations will just have to be reolved bu pencil and paper and a supply of erasures To blatantly impose this coordinate structure absent the courtesy of an explanation in terms of experimental results would be a form of insulting heresy, Heresy, now,by itself iself is, contrary to some popular opinions ,just like the baby bear's porridge, not too hot bot too cold, but just right. Yuriy you rescue SR only by burying it in practiced confusion. The mesuremnent system I have been spreading for some months now is by your activityh a recognition]] of its worth and value. This is so because you cannot rescue SR by invoking the postulate that it is impossoible to detect or measure the unaccelerated translatory motion of an inertiak system in free space because we both know now it is a trivial exercise to measure the contributions of the system;'s inertial velocity components. Yuriy, you would not have suffered all the recent slings and arrows of outrageous forces in your sea of troubles unless yiu had observed the demise of an erstwhile lkimiting special realtivity theaohy when excised from your thought Please Register or Log in to view the hidden image! when falling on your mental .sword of physical law.