[Figs. 366-377]
An examination of figure 372 shows that it is a whorl. In order to classify the ridge tracing accurately, however, so that the fingerprint card can be placed in the correct classification, the left delta must show. The approximate ridge tracing for the whorl in figure 372 would be Meeting. An examination of the properly taken fingerprint in figure 373 indicates that the correct ridge tracing is Inner. It follows that the pattern in figure 372 would not have been placed in the proper place in file.
The correct whorl tracing is needed to obtain the complete subsecondary and the major classifications.
It may be noted that both deltas are present in figure 374. This would enable the technical expert to ascertain the correct ridge tracing, Outer. In the core of the whorl, however, there is a heavy amount of ink which makes it impossible to determine the type of whorl with any degree of accuracy. If one were to hazard a guess, it would appear to be a plain whorl. Actually, the correct type of whorl, a double loop, is clearly visible in figure 375.
It can be ascertained that the pattern in figure 376 is a loop, but an accurate ridge count cannot be obtained because the left delta does not appear. The approximate ridge count of this loop is 14 to 16. This approximation is sufficient for a fingerprint expert to place this loop in the "O" group of any finger of the subsecondary. The correct ridge count of this loop is 19, and it appears in illustration 377. The approximate ridge count is not sufficient to place this print properly in the large files of the FBI because in certain general complete classification formulas the accurate ridge count is needed to obtain an extension. These extensions use a smaller grouping of ridge counts to form a valuation table, and in this way, differ from the larger grouping of ridge counts which form the basis of the subsecondary classification. These extensions are called the second subsecondary and the special loop extension and are outlined in [chapter VI].
There are two additional points which illustrate the FBI's need for the delta, ridges, and core to show clearly in loops. The first point is set forth: the ridge count of the loop may be needed to obtain the key classification. The key classification is an actual ridge count, and no valuation table is used to obtain a subdivision. The key classification is used as an integral part of the fingerprint filing system. The second point is as follows: the ridge count may be needed to obtain the final classification. The final classification is an actual ridge count, and no valuation table is used to obtain a subdivision. The final classification is used as an integral part of the fingerprint filing system.
The following are just a few examples to illustrate the completeness of the classification formula used in the FBI fingerprint file:
| 12 | M | 9 | R | OIO | 11 |
| S | 1 | R | IOI | ||
| Key | Major | Primary | Secondary | Subsecondary | Final |
| 6 | 17 | aW | IIO | 9 | |
| 1 | U | OII | |||
| Key | Primary | Small Letter Secondary | Subsecondary | Final |