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).
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.
When the ridge traced ends abruptly, and it is determined that the
ridge definitely ends, the tracing drops down to the point on the next
lower ridge immediately beneath the point where the ridge above ends,
continuing from there. Figure 291, therefore, is an outer whorl.
In this connection it should be noted that the rule for dropping to
the next lower line applies only when the ridge definitely ends.
Short breaks in a ridge which may be due to improper inking, the
presence of foreign matter on the ridges, enlarged pores, disease, or
worn ridges should not be considered as definite ridge endings. The
determination of what constitutes a definite ending will depend, of
course, upon the good judgment of the classifier. When the question
arises as to whether a break encountered in the ridge tracing is a
definite ending, or whether there has been interference with a natural
impression, the whole pattern should be examined to ascertain whether
such breaks are general throughout the pattern. If they are found to
be common, consideration should then be given to the possibility that
the break is not a definite ridge ending. Appropriate reference
tracing should be done in all such cases.
Whenever the ridge traced bifurcates, the rule for tracing requires
that the lower limb or branch proceeding from the bifurcation be
followed. This is illustrated in 292.
Accidentals often possess three or more deltas. In tracing them only
the extreme deltas are considered, the tracing beginning at the
extreme left delta and proceeding toward the extreme right delta, as
illustrated in figure 293.
In a double loop or accidental the problem of where to stop tracing is
sometimes presented. The rule is, when the tracing passes inside of
the right delta, stop at the nearest point to the right delta on the
upward trend, as in figure 294. If no upward trend is present,
continue tracing until a point opposite the right delta, or the delta
itself, is reached (figs. 295 and 296).