http://www.amazon.com/Relativity-Its.../dp/0486406768
Relativity and Its Roots, Banesh Hoffmann, p. 105: "In one case your clock is checked against two of mine, while in the other case my clock is checked against two of yours, and this permits us each to find without contradiction that the other's clocks go more slowly than his own."

Einsteiniana's scenarios allow the travelling twin's clock to be checked against two clocks in the sedentary twin's system - e.g. clocks situated at the initial and final points of the travelling twin's trip. However Einsteiniana's scenarios NEVER allow the sedentary twin's clock to be checked against two clocks in the travelling twin's system - e.g. clocks situated at the front and back ends of a (very long) rocket. Such biased scenarios convert the RECIPROCAL time dilation predicted by special relativity into an asymmetric time dilation - the travelling twin always returns younger so that Einsteinians can sing "Yes we all believe in relativity, relativity, relativity" and go into convulsions.

It is easy to imagine a scenario in which, while the travelling twin performs the forward part of trip, the sedentary twin's clock effectively moves from the front end to the back end of a (very long) rocket. Then, as the travelling twin returns, the sedentary twin's clock effectively moves from the back end to the front end of the rocket.

In this scenario time dilation is RECIPROCAL again and special relativity gloriously predicts that, when the brothers finally meet, either of them is younger than the other.

Pentcho Valev