  We associate the following physical co-mover conditions of to different frame
choices: i) Eckart: particle flow, ii) Landau-Lifshitz: energy flow, iii)
J\"uttner: moving thermometer frame. The role of fixing a flow-frame is
analysed with respect to local equilibrium concentrating on dissipative
currents and forces in single component relativistic fluids. The special role
of a "J\"uttner frame" is explored and contrasted to the more common Eckart and
Landau-Lifshitz choices.
