  We present a system of X-ray photometry for the Chandra satellite. X-ray
photometry can be a powerful tool to obtain flux estimates, hardness ratios,
and colors unbiased by assumptions about spectral shape and independent of
temporal and spatial changes in instrument characteristics. The system we have
developed relies on our knowledge of effective area and the energy-to-channel
conversion to construct filters similar to photometric filters in the optical
bandpass. We show that the filters are well behaved functions of energy and
that this X-ray photometric system is able to reconstruct fluxes to within
about 20%, without color corrections, for non-pathological spectra. Even in the
worst cases it is better than 50%. Our method also treats errors in a
consistent manner, both statistical as well as systematic.
