Abstract
The KM3NeT detectors are large three-dimensional arrays of several thousands digital optical modules under construction in the Mediterranean Sea. The basic detection element of the neutrino telescope is the digital optical module containing 31 three-inch photomultiplier tubes. Each detection unit, composed of 18 digital optical modules, is a mechanical structure anchored to the sea floor, held vertical by a submerged buoy for the detection of Cherenkov light emitted by charged secondary particles emerging from neutrino interactions. Detector calibration, i.e. timing, positioning and sea-water properties, is overviewed in this talk and discussed in detail in this conference.