  After initial tests performed during previous observing runs, a Newtonian
Calibrator (NCal) system was developed and installed on the Virgo gravitational
wave detector for the O4 observing run. This system, which is continuously
operated, provides the absolute calibration of Virgo for this run. Its
uncertainty of 0.17% on the amplitudes of the injected signals is better than
that obtained with other calibration techniques like the photon calibrator
(PCal). This paper presents this NCal system and details the different sources
of uncertainties.
