Reference device (1) for real-time tracking of bone and/or surgical objects in computer-assisted surgery, the device (1) comprising: A) an upper member (2) having at least one circular cylindrical hole (3) penetrating through the upper member (2) from the upper surface (5) to the lower surface (6), wherein the hole (3) defines a circular cylindrical reference element (15) having a diameter d and a height h, the ratio between the diameter d and the height h of the reference element (15) is minimum 1/3, and B) a lower member (4) configured to cover the lower orifices (8) of the holes (3)； and wherein C) the upper member (2) is configured as a plate shaped body.
