  We present results from in-flight calibration of the High Energy Transmission
Grating Spectrometer (HETGS) on the Chandra X-ray Observatory. Basic grating
assembly parameters such as orientation and average grating period were
measured using emission line sources. These sources were also used to determine
the locations of individual CCDs within the flight detector. The line response
function (LRF) was modeled in detail using an instrument simulator based on
pre-flight measurements of the grating alignments and periods. These LRF
predictions agree very well with in-flight observations of sources with narrow
emission lines. Using bright continuum sources, we test the consistency of the
detector quantum efficiencies by comparing positive orders to negative orders.
