The Milagro detector is an air shower array which uses the water Cherenkov
technique and is capable of continuously monitoring the sky at energies near 1
TeV. The detector consists of 20000 metric tons of pure water instrumented with
723 photo-multiplier tubes (PMTs). The PMTs are arranged in a two-layer
structure on a lattice of 3 m spacing covering 5000 $m^2$ area. The direction
of the shower is determined from the relative timing of the PMT signals,
necessitating a common time reference and amplitude slewing corrections to
improve the time resolution. The calibration system to provide these consists
of a pulsed laser driving 30 diffusing light sources deployed in the pond to
allow cross-calibration of the PMTs. The system is capable of calibrating times
and the pulse-heights from the PMTs using the time-over-threshold technique.
The absolute energy scale is provided using single muons passing through the
detector. The description of the calibration system of the Milagro detector and
its prototype Milagrito will be presented.
