The apparent plunges of inclined drill holes and linear geological structures which perforate or approach a vertical cross-section obliquely should be shown accurately for correct data representation. Much time can be saved by using a graph or a slide-rule computer to determine the apparent angles of linear elements. The 2 mapping aids are based on the relationship tan gamma = tan alpha /cos beta where alpha is the angle of plunge, beta is the angle of convergence, and gamma is the apparent inclination.

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