Recently a suggestion has been made that standard textbook representations of hypersurfaces of simultaneity for the travelling twin in the twin 'paradox' are incorrect. This suggestion is false: the standard textbooks are in agreement with a proper understanding of the relativity of simultaneity.

Hans C. Ohanian 1 claims to “defeat” the conventionalist thesis of clock synchronization using an argument based on dynamics. My aim here is to show that his argument does not succeed.