Too much stress cannot be placed upon the necessity of referencing questionable patterns, whether it be in the interpretation of the type of pattern, the ridge count, or the tracing.
The factors which make it necessary are: variation in individual judgment and eyesight, the amount of ink used, the amount of pressure used in taking the prints, the difference in width of the rolled impressions, skin diseases, worn ridges due to age or occupations, temporary and permanent scars, bandaged fingers, crippled hands, and amputation.
For the highest degree of accuracy, all rolled impressions should be checked by the plain impressions, which generally are not distorted by pressure. This also helps prevent error caused by the reversal or mixing of the rolled impressions out of their proper order. For the same reason, as much of the counting and tracing should be done in the plain impressions as it is possible to do.
If there is any doubt as to which of two or more classifications should be assigned to a given pattern, it is given the preferred classification and reference searches are conducted in all other possible classifications. For example, if on a print with the preferred classification
| 1 A |
| 1 Aa |
it is questionable whether the left middle finger should be a plain arch, a tented arch, or a radial loop, the print is searched in the
| 1 A |
| 1 Aa |
group, and reference searches are conducted in the
| 1 A |
| 1 At |
and