(hod’ d∂ gram) 1. The figure described by the terminus of a moving vector. 2. A plot of the motion of a point as a function of time, that is, a display of a particle path especially with multicomponent detectors. Used to determine the direction of a wave’s approach to the detectors and, with borehole geophones, the orientation of the detectors. See Figure R-3. 3. A time-distance curve.