1. The difference between the two-way travel times of reflected energy detected at two geophone offset distances.

2. (normal moveout, NMO, Δ‎T) At an offset distance x, the difference in two-way travel time between the detected reflection event at x (t_x) and at zero offset (t_o), such that Δ‎T = t_x - t_o ≈ x²/(2V²t_o), where V is the seismic velocity of the medium above the reflector.

3. (dip moveout, DMO, Δ‎T_d) In the case of a planar dipping reflector, the difference between the moveout updip and downdip, proportional to the angle of dip θ‎, such that: Δ‎T_d = 2xsin θ‎/V, where x is the offset distance from the mid-point.