  AGILE is a mission of the Italian Space Agency (ASI) Scientific Program
dedicated to gamma-ray astrophysics, operating in a low Earth orbit since April
23, 2007. It is designed to be a very light and compact instrument, capable of
simultaneously detecting and imaging photons in the 18 keV to 60 keV X-ray
energy band and in the 30 MeV{50 GeV gamma-ray energy with a good angular
resolution (< 1 deg at 1 GeV). The core of the instrument is the Silicon
Tracker complemented with a CsI calorimeter and a AntiCoincidence system
forming the Gamma Ray Imaging Detector (GRID). Before launch, the GRID needed
on-ground calibration with a tagged gamma-ray beam to estimate its performance
and validate the Monte Carlo simulation. The GRID was calibrated using a tagged
gamma-ray beam with energy up to 500 MeV at the Beam Test Facilities at the
INFN Laboratori Nazionali di Frascati. These data are used to validate a GEANT3
based simulation by comparing the data and the Monte Carlo simulation by
measuring the angular and energy resolutions. The GRID angular and energy
resolutions obtained using the beam agree well with the Monte Carlo simulation.
Therefore the simulation can be used to simulate the same performance on-light
with high reliability.
