  Stellar Doppler velocimetry determines a star's radial velocity $v_r$ via
measurement of a redshift, $z$. At precisions below 10 m s$^{-1}$ conversion
between the two quantities is complex, and care must be taken to properly
account for the effects of relativity. One particular aspect of the problem
that bears repeating is that the one-dimensional version of the relativistic
Doppler formula, which does not distinguish between the motion of the source
and the observer, is incorrect in this context, and indeed does not even
provide the correct coefficient for variations in the second-order terms
involving $\beta$. Nonetheless, it is often useful to report a redshift in the
more familiar units of velocity without a rigorous calculation, and much code
already exists that does this. In these cases it is important to clearly
document which formula is being used, and I recommend simply (and explicitly)
using the approximation $v_r \approx cz$. This choice is trivially inverted,
does not misrepresent the degree of relativistic rigor that has been applied in
translating between redshift and radial velocity, and is, I believe, the most
commonly followed convention in astronomy and cosmology.
  I also briefly discuss the differences between the Wright & Eastman
barycentric correction procedure and the Lindegren & Dravins barycentric radial
velocity measure.
