The entries in Table XII. are derived from a catalogue of 500 sets, and include all entries that appeared more than five times; in other words, whose frequency exceeded 1 per cent. These are the index-headings that give enough trouble to deserve notice in catalogues of, say, from 500 to 1000 sets. In the left half of Table XII. all the index-headings are given, under each of which more than 1 per cent of the sets fell, when the method of "_i_ and _o_ in fore-fingers" was adopted; also the respective percentage of the cases that fell under them. In the right half of the table are the corresponding index-headings, together with the percentages of frequency, when the "no slope" method is employed. These are distinguished by Roman numerals. The great advantage of the "_i_ and _o_ fore-finger" method lies in its power of breaking up certain large groups which are very troublesome to deal with by the "no slope" method. According to the latter as many as 9.2 per cent of all the entries fall under the index-heading marked III., but according to the "_i-o_ fore-finger" method these are distributed among the headings 3, 4, and 5. The "all slopes" method has the peculiar merit of breaking up the large group Nos. 11 and VIII. of "all whorls," but its importance is not great on that account, as whorls are distinguishable by their cores, which are less troublesome to observe than their slopes. The percentage of all the entries that fall under a single index-heading, according to the "_i-o_ fore-finger" method, diminishes with the number of entries at the following rate:-- TABLE XIII. +----------------------------------------------------------+ | | Total number of entries. | | |--------------------------| | | 100 | 300 | 500 | |-------------------------------|--------|--------|--------| | Percentage of entries falling | | | | | under a single head | 63 | 49.0 | 39.8 | +----------------------------------------------------------+ It may be that every one of the 4{2} x 3{8}, or one hundred and five thousand possible varieties of index-headings, according to the "_i-o_ fore-finger" method, may occur in Nature, but there is much probability that some of them may be so rare that instances of no entry under certain heads would appear in the register, even of an enormous number of persons. * * * * * Hitherto we have supposed that prints of the ten fingers have in each case been indexed. The question now to be considered is the gain through dealing in each case with all ten digits, instead of following the easier practice of regarding only a few of them. The following table, drawn up from the hundred cases by the "all slopes" method, will show its amount. TABLE XIV.--_From 100 Sets._