Abstract: An extendible surveying probe comprises two collinear position detecting units that allow the probe to be used in an inclined position for accessing vertically inaccessible points with a tip thereof. The two position detecting units may consist of two GPS or GLONASS units used in association with another GPS or GLONASS unit installed on a known point or, alternatively, of two corner cubes used in association with a ground total station. The position detecting units provide spatial coordinates of two spaced-apart collinear points which may be used to extrapolate the coordinates of the point in contact with the tip of the probe.

Abstract: A simulator, for use with stereoradiographs, as a neurosurgical aid in locating potential paths for the implantation of probes in selected locations of the brain. It has a support, on the top surface of which is mounted a pair of radiographs disposed for stereoscopic viewing. An elongated ruler lies over the stereoradiographs and is movable in translation over them. A pair of transparent flat plotting plates are mounted on the ruler and are slidable therealong. Each plotting plate has a circular hole and a transparent circular disc is rotatable around this hole; a radial line extending from the center of the disc giving a "floating line" in the stereoscopically viewed model to simulate a probe to be implanted in the brain.