A number of techniques for determining stellar radial velocities with a precision better than 100 m s-1 are now becoming available. Three types of precision velocity techniques have been proposed, using for wavelength reference either telluric lines, Fabry-Perot fringes, or lines generated in an absorption cell. The author has used the latter technique, with a hydrogen fluoride cell, to obtain time series observations of Procyon on three nights. The internal error in these velocities is 10 m s-1, and the mean night-to-night difference is about 6 m s-1. These results suggest that the HF technique has good long-term stability, and therefore can be applied to the search for sub-stellar mass companions to solar-type stars.