These devices can be used with the Zoeppritz equations to perform AVO analysis. In some configurations, these devices flatten a hyperbolic signal by correcting for the normal moveout time. Many of these devices are spaced symmetrically (15[1])on either side of a shot point in the split-spread method, which often produces lower signal-to-noise ratios than the common mid-point method. The broadband class of these devices have a larger range than their long-period and short-period types and use a negative feedback system to restrict the motion of an inertial (*) pendulum. The “shadow zone” is a blind spot for these devices, which historically used a rotating drum wrapped in a sheet of paper, allowing a pen to draw wiggly lines in response to stimuli like P and S waves. For 10 points, name these devices used to record earthquakes. ■END■