  There is a quantitative error in the derivation for the spin decoherence rate
by Talman in IPAC2012. The crucial point is a subtle confusion between the
concept of `longitudinal' as in `along the reference orbit' and `parallel to
the particle velocity.' They are $\it not$ the same direction, and the
distinction is significant for high-precision experiments to search for a
possible nonzero electric dipole moment (EDM) of a charged particle in a
storage ring.
