Classification, and the Henry System

In one line

Classification turns ten fingerprints into a short expression that tells a searcher which drawer to open.

In the wording a student can write in an exam: the Henry system of classification, developed in Bengal by Edward Richard Henry with Azizul Haque and Hem Chandra Bose, reduces a set of ten fingerprints to a formula of which the primary classification is the best known part; the ten fingers are numbered from the right thumb to the left little finger, the fingers are taken in pairs, and each pair is assigned a value of 16, 8, 4, 2 and 1 respectively; a finger is counted only if its pattern is a whorl; the values of the whorls on the even numbered fingers are added and one is added to the total to give the numerator, the values of the whorls on the odd numbered fingers are added and one is added to give the denominator, and the resulting fraction is the primary classification; and further subdivisions, the secondary, sub-secondary, major, final and key classifications, narrow the group further.

Why a formula was needed

A collection of ten-print slips is useless unless a searcher can find the right one. Comparing a new slip with each of a hundred thousand others is impossible by hand. The formula converts each slip into an address, so the search is against a few dozen slips rather than the whole collection.

That is the Indian contribution to the subject, and it is why the world's first Finger Print Bureau was at the Writers' Building in Calcutta in 1897.

The primary classification, worked

Step one, number the fingers. From 1 to 10, beginning with the right thumb and ending with the left little finger.

Step two, assign the pair values. The fingers are taken in pairs and each pair carries a value: fingers 1 and 2 are worth 16, fingers 3 and 4 are worth 8, fingers 5 and 6 are worth 4, fingers 7 and 8 are worth 2, and fingers 9 and 10 are worth 1.

Step three, count only whorls. A finger contributes its value only if its pattern is a whorl. Loops and arches contribute nothing.

Step four, the numerator and denominator. Add the values of the whorls on the even numbered fingers, being 2, 4, 6, 8 and 10, and add one. That is the numerator. Add the values of the whorls on the odd numbered fingers, being 1, 3, 5, 7 and 9, and add one. That is the denominator.