1. An apparatus for determining an inclination angle θ between an axis of an elongate object contacting a plane surface with a tip and a normal to said plane surface, said apparatus comprising: a) an emitter on said elongate object for illuminating said plane surface with a probe radiation at an angle σ to said axis; b) a detector on said elongate object for detecting a radiation characteristic of a scattered portion of said probe radiation returning from said plane surface; and c) a computing unit for deriving said inclination angle θ from said radiation characteristic.