A hand-held manual surgical instrument intended to be used during insertion of an electrode array into the cochlea during implantation of a cochlear implant, to determine the number of active bands that can be implanted, to measure insertion depth, and sometimes to assess cochlear lumen patency. It consists of a thin probe with depth markings mounted on a handle, made of metal [e.g., platinum (Pt)] and synthetic polymers (e.g., silicone). This is a single-use device.