  The flux, polarimetric and spectral response of phased array radio telescopes
with no moving parts such as LOFAR is known to vary considerably with
orientation of the source to the receivers. Calibration models exist for this
dependency such as those that are used in the LOFAR pipeline. Presented here is
a system for comparing the predicted outputs from any given model with the
results of an observation. In this paper, a sample observation of a bright
source, Cassiopeia A, is used to demonstrate the software in operation, by
providing an observation and a model of that observation which can be compared
with one another. The package presented here is flexible to allow it to be used
with other models and sources. The system operates by first calculating the
predictions of the model and the results of an observation of linear fluxes and
Stokes parameters separately. The model and observed values are then joined
using the variables common to both, time and frequency. Normalisation and RFI
excision are carried out and the differences between the prediction and the
observation are calculated. A wide selection of 2-, 3- and 4-dimensional plots
are generated to illustrate the dependence of the model and the observation as
well as the difference between them on independent parameters time, frequency,
altitude and azimuth. Thus, beamModelTester provides a framework by which it is
possible to calibrate and propose refinements to models and to compare models
with one another.
