  We report moderate magnetic flux of 450G < Bf < 750G (3sigma) on the nearby
M5.5 flare star Proxima Centauri. A high resolution UVES spectrum was used to
measure magnetic flux from Zeeman broadening in absorption lines of molecular
FeH around 1mu. The magnetic flux we find is relatively weak compared with
classical strong flare stars, but so are Proxima's flaring rates and actual
emission levels. We compare what is known about the rotation rate, Rossby
number, and activity levels in this star to relations between these quantities
that have been recently being developed more generally for M dwarfs. We
conclude that the magnetic flux is higher than the best estimates of the Rossby
number from period measurements. On the other hand, the activity levels on
Proxima Centauri are at the high end of what could be expected based on the
measured field, but not so high as to exceed the natural scatter in these
relations (other stars lie along this high envelope as well).
