  Observations of X-ray cavities formed by powerful jets from AGN in galaxy
cluster cores are commonly used to estimate the mechanical luminosity of these
sources. We test the reliability of observationally measuring this power with
synthetic X-ray observations of 3-D MHD simulations of jets in a galaxy cluster
environment. We address the role that factors such as jet intermittency and
orientation of the jets on the sky have on the reliability of observational
measurements of cavity enthalpy and age. An estimate of the errors in these
quantities can be made by directly comparing ``observationally'' derived values
with values from the simulations. In our tests, cavity enthalpy, age and
mechanical luminosity derived from observations are within a factor of two of
the simulation values.
