We present an analysis of astrometric data from FGS 3 , a white-light interferometer on HST , and of radial velocity data from two ground-based campaigns .
We model the astrometric and radial velocity measurements simultaneously to obtain parallax , proper motion and component masses for Wolf 1062 = Gl 748 AB ( M3.5V ) .
To derive the mass fraction , we relate FGS 3 fringe scanning observations of the science target to a reference frame provided by fringe tracking observations of a surrounding star field .

We obtain an absolute parallax \pi _ { abs } = 98.0 \pm 0.4 milliseconds of arc , yielding { \cal M } _ { A } = 0.379 \pm 0.005 { \cal M } _ { \hbox { $ \odot$ } } and { \cal M } _ { B } = 0.192 \pm 0.003 { \cal M } _ { \hbox { $ \odot$ } } , high quality component masses with errors of only 1.5 % .