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Compiles lists of events from photographs of bubble chamber, cloud chamber, or other particle detector, and operates machine to record characteristics of events into computers: Observes projected photographs to locate particle tracks, locate and count events indicated by tracks, and identify nature of observed events. Receives instructions from scientist directing project as to specific events that are important in experiment, and identifies such events from other events. Turns cranks to move projector and locates point on track under crosshairs of eyepiece. Enters data into computer to record coordinates of particles. Repeats process to record successive stages of tracks resulting from each event to provide information for scientists to identify particles. May use microscope fitted with scales and protractors to scan photographic emulsions previously exposed to direct radiation and to compute direction, angle, length, curvature, density, and depth of tracks from standard formulas.