Abstract: A probe position sensing system for accurately determining a spatial location in a coordinate system of a distal end of a probe assembly. The probe assembly includes an articulated arm having a pair of sections interconnected by a flexible joint and at least one element. The element extends through the joint and is positioned to be subjected to a degree of flexure due to relative displacement of the sections. A flexure of the element induces a change in a physical property associated with the element. An instrument monitors the physical property and derives an angle between adjacent sections from variations of the physical property.