Tony Maughan told me that the centres were not to be relied on and that rollers were the best bet. Cheers, Stu.
Terry Prince told me the same thing about his cranks. And I quote “The crank cannot be checked between centres on a lathe, only on knife edges close to the inner bearings as the grinding process does not use the centres and they could be out.”
However, there is a local guru here that I would trust to measure one between centres. As I understand it, he confirms the centres are actually centres and redoes them if they are not.