  We present analysis of commissioning $M-$band data acquired with the infrared
echelle spectrograph (iSHELL) on {\it NASA's Infrared Telescope Facility}. In
this paper we describe the delivered performance of the instrument for these
$M-$band observations and the data reduction process. The feasibility of using
iSHELL for spectro-astrometry is tested on the Herbig Ae/Be star HD~179218 and
we show that sub-milliarcsecond fidelity is achievable.
