Velocity calculated from normal-moveout measurements and a constant-velocity model. Used to maximize events in common-midpoint stacking. Sometimes erroneously called ‘‘rms velocity.’’ Usually calculated for the best-fit hyperbola to gather data, the value thus depending somewhat on the range of offsets involved. Fitting an NMO equation to CMP data is equivalent to assuming an ellipsoidal wavefront, yielding the stacking velocity of the horizontal component. Nonelliptical wavefronts yield offset-variable stacking velocities. See velocity analysis.