=2.3 m
s-1. Note that a correction is done to suppress a slight mismatch
between the two optical paths: 
Vr(sky) =
Vr(star)-.04\Vr(star)+0.6 (Vr is the velocity
variation of the spectrograph in units of m s-1). (b) histogram
of the variation of the spectrograph monitor by the star-way during the
measurements.