In a delta structure, three directions of ridge flow converge at one point. This may happen on intersecting ridges, in a valley, or on some combination of the two. The location of the delta is that center point. Use a radius of uncertainty if you cannot precisely determine the location, whether because of poor image quality or an ambiguous delta structure.
Mark the directions of the delta in the three directions of ridge flow. When orientation is known, mark the direction closest to upright first, and mark the next direction counterclockwise (i.e. to the left) second. If necessary, add a range of direction uncertainty for each direction.
Fingerprints with a loop or whorl pattern will always have a delta or deltas. Tented arches sometimes have a delta that needs to be marked. Accidental whorls may have any number of deltas. On palm impressions, carpal and interdigital deltas should be marked. On other friction ridge skin impressions, delta-like patterns may be marked as deltas.
In the special case that the delta cannot be seen in the impression but you can make a reasonable estimate of its location, you may mark the delta in the approximate location. Include an appropriately large radius of uncertainty.
