Embodiments of the invention relate to an ancillary surgical instrument including at least a first contact point to come into contact with a first reference point of an operating area； a second contact point intended to come into contact with a second reference point of the operating area； a contact area intended to come into contact with a third reference point of the operating area； a determination unit for determining an orientation reference of the ancillary instrument in a Galilean orientation reference； and a communication unit for communication the determined orientation reference.
