Computation charts are presented which reduce or eliminate calculations of correlation and wave-front depth charts. A series of depth charts are made for particular values of the velocity increment solving the time-depth relation for all possible initial velocities of the equation y = (V 0 /k) (e kt -1). From these charts, the average velocity-depth curves are obtained, and also the velocity function to be used on a project determined from velocity shooting by comparison to the theoretical average velocity-depth curves. For wave-front depth charts, a series of families of curves are plotted for the full range of velocity increments and all initial velocities for the equations of the instantaneous center of the wave front, z = (V 0 /k) (cosh kt/2-1), and the radius of the wave front, r = (V 0 /k) (sinh kt/2). The relation between k and e kt 2/ for a range of times is plotted, and therefrom the value of e kt 2/ obtained for the particular velocity increment for the solution of the equation tan theta /2 = tan theta 0 /2.e kt 2/. Finally, curves for a series of tan theta /2 against initial velocity curves are plotted for a series of step out times, and therefrom the value of tan theta /2 = tan theta 0 /2.e kt 2/, or the angle of dip, theta , is obtained. This latter family of curves can be used to determine the variation of dip with variation in initial velocity in highly folded areas. The latter set of curves is useful for the construction of a time-step-out time-dip-depth-offset chart which is used for direct plotting of offset-depth-dip positions of reflecting horizons, or as a trace-analysis underlay chart.

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