. Deep borehole surveys and problems. Boring. 276 DEEP BOREHOLE SURVEYS AND PROBLEMS ^Off Vertical Angle NOMOGRAPHIC AND ALIGNMENT METHODS These simple and easily understood charts are becoming more and more popular because they can, as a rule, be manipulated by the boring personnel and others who wish to save time. Figure 185^ shows the well-known versed-sine relation which can be applied to a hole the deviation of which is either regular or can be approximately meaned throughout its course, giving a straight deflection; that is to say, a constant off-vertical angle. The alignment chart itsel
. Deep borehole surveys and problems. Boring. 276 DEEP BOREHOLE SURVEYS AND PROBLEMS ^Off Vertical Angle NOMOGRAPHIC AND ALIGNMENT METHODS These simple and easily understood charts are becoming more and more popular because they can, as a rule, be manipulated by the boring personnel and others who wish to save time. Figure 185^ shows the well-known versed-sine relation which can be applied to a hole the deviation of which is either regular or can be approximately meaned throughout its course, giving a straight deflection; that is to say, a constant off-vertical angle. The alignment chart itself (Fig. 186) is constructed by putting on the left the logarithmic scale A with the scale of versed sines Bi or Ci on its right and the vertical correction scales corresponding at B2 and Co- To get a correction, place a straightedge at the desired depth of hole on A scale, say 100 ft., and at the proper off-vertical angle on Bi scale; continue and read off the correction on B2 or C'z scale. If the straightedge falls off scale B2, then use scales Ci and C2. If the measured depth is greater than scale A divide it by 10 and multiply the corresponding results on B2 or C2 by 10. Thus if the depth is 2,500 ft. and the off-vertical angle 10 deg. use 250 ft. and multiply the resultant vertical correction of ft. by 10, giving ft. Use a transparent cellu- loid straightedge with a fine black parallel line near one edge. Based on Fig. 185 Mr. BrindeP discusses a simple employ- ment of mathematical tables and formula, noting that 1. By the Cosine Method. The corrected measurement = (actual measurement) X (cosine of off-vertical angle), , in Fig. 185 AB = AD cos BAD. 1 Brindel, H. F., Oil Gas Jour., p. 41, Apr. 11, 1929. 2 Ibid., p. Fig. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Haddock, M.
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