A method for harmonizing an equipment relative to a vehicle, such as a helicopter, based upon sensing of the gravitational field in a number of reference systems. The equipment is installed fixedly on board the vehicle which, relative to a first absolute reference system (RM), has an orientation defined by a second reference system (R2) tied to the vehicle. The equipment is subjected to the earth's gravitational field represented by a gravity vector g oriented along its gradient. The orientation of the equipment is defined, relative to the first absolute reference system (RM), by a third reference system (R3). The equipment includes a device for measuring the components of the gravity vector g, and the vehicle carries a computer, a memory associated with the computer; and a link connecting the equipment to the computer and to the memory. The gravitational field is measured when the vehicle is in a number of different orientations, and the equipment is harmonized to the vehicle based thereon.