  We compared the frequency shift of the 21Ne Zeeman resonance induced by
polarized Rb vapor to the shift induced in the 3He Zeeman resonance. The 3He/Rb
shift has recently been measured with high precision, permitting the conversion
of our differential measurement to an absolute value for the 21Ne/Rb shift. We
report a value of K = 31.8 +/- 2.8 for the Rb/21Ne enhancement factor at a
temperature of 124.8 +/- 1.9 C. We propose high-precision differential contact
shift measurements, the absolute accuracy of which would be limited by the
error in the 3He contact shift.
