  We present a blind comparison of two methods to measure the mean surface
magnetic field strength of the classical T Tauri star CI Tau based on Zeeman
broadening of sensitive spectral lines. Our approach takes advantage of the
greater Zeeman broadening at near-infrared compared to optical wavelengths. We
analyze a high signal-to-noise, high spectral resolution spectrum from
1.5-2.5um observed with IGRINS (Immersion GRating INfrared Spectrometer) on the
Discovery Channel Telescope. Both stellar parameterization with MoogStokes
(which assumes an uniform magnetic field) and modeling with SYNTHMAG (which
includes a distribution of magnetic field strengths) yield consistent
measurements for the mean magnetic field strength of CI Tau is B of ~2.2 kG.
This value is typical compared with measurements for other young T Tauri stars
and provides an important contribution to the existing sample given it is the
only known developed planetary system hosted by a young classical T Tauri star.
Moreover, we potentially identify an interesting and suggestive trend when
plotting the effective temperature and the mean magnetic field strength of T
Tauri stars. While a larger sample is needed for confirmation, this trend
appears only for a subset of the sample, which may have implications regarding
the magnetic field generation.
