[Figs. 269-279]
Some whorls may be found which contain ridges conforming to more than one of the whorl subdivisions described. In such cases, the order of preference (if any practical distinction need be made) should be: (1) accidental, (2) double loop, (3) central pocket loop, (4) plain whorl.
Whorl tracing
The technique of whorl tracing depends upon the establishment of the focal points—the deltas. Every whorl has two or more. When the deltas have been located, the ridge emanating from the lower side or point of the extreme left delta is traced until the point nearest or opposite the extreme right delta is reached. The number of ridges intervening between the tracing ridge and the right delta are then counted. If the ridge traced passes inside of (above) the right delta, and three or more ridges intervene between the tracing ridge and the delta, the tracing is designated as an "inner"—I (fig. 280). If the ridge traced passes outside (below) the right delta, and three or more ridges intervene between the tracing ridge and the right delta, the tracing is designated as an "outer"—O (fig. 281). All other tracings are designated as "meeting"—M (figs. 282 to 287).
[Figs. 280-287]
Tracing begins from the left delta. In no instance is a tracing to begin on a type line. In figure 288, tracing begins at the short ridge which is the left delta. It is true that inasmuch as the short ridge ends immediately the type line is next followed, but this is only because the type line is the next lower ridge. Its status as a type line is independent and has no bearing on the fact that it is being traced. This point is illustrated further in figure 289. This pattern shows an inner tracing. It will be noted that the delta is at the point on the first recurve nearest to the center of the divergence of the type lines. It will be further noted that tracing begins at the point of delta on the left and continues toward the right, passing inside of the right delta, with three ridges intervening between the tracing ridge and the right delta. This shows the tracing to be an inner tracing. If, in this case, the type line were traced (which would be the incorrect procedure), only two ridges would intervene between the tracing ridge and the right delta, resulting in an erroneous meeting tracing. Figure 290 is another example of the application of this rule. This illustration is also an inner whorl.