Using Co-60 gamma-ray anisotropy radiation as a primary thermometer, w
ith a Pt NMR susceptibility secondary thermometer, we have made high-p
recision measurements of the He-3 melting pressure versus temperature
from 500 mu K to 25 mK. Temperatures obtained for the fixed points on
the melting curve are: the superfluid A transition T-A = 2.505 mK, the
A-B transition T-AB = 1.948 mK, and the solid ordering temperature T-
N = 0.934 mK. We provide a functional form for P(T), which, with the f
ixed points, constitutes a convenient temperature scale, based on a pr
imary thermometer, usable to well below 1 mK.