There are two general plans of indexing the card ledger—alphabetical and numerical. The alphabetical method consists of a set of guide or index cards between which the cards are filed. This index may consist of one index for each letter of the alphabet, a smaller number with two or more letters on one index, or a much larger number subdividing the alphabet into as many parts as may be necessary. In planning an index for a card ledger, a safe rule to follow is to provide one index card for every ten ledger cards. [Illustration: Fig. 21 _b._ Ledger Card for Publishers ] A subdivision of the alphabetical index is the geographical or territorial. This divides the ledger by states and towns. Guide cards, printed with the names of the states, provide the main division; other guides, printed with names of towns, subdivide the state sections; and where necessary, alphabetical guides subdivide the names in the towns. If desired, the ledger may be divided into territorial sections, as East and West; or each section may include the territory covered by one salesman. A numerical index divides the cards by tens and hundreds. Guide cards numbered by hundreds—100, 200, etc.—provide the main divisions. Between these are placed guides numbered 10, 20, 30, etc. to subdivide these sections by tens, and the ledger cards are filed in numerical order between these guides. To facilitate locating any number desired, the cards themselves are made with small projections numbered from 0 to 9 to represent the units. Each card bears one tab, and all tabs bearing the same unit are in the same relative position on the card; that is—0 is always at the extreme left, while 9 is ten positions to the right. When the cards are placed in numerical sequence, between the guides numbered by 10's, any number can be found instantly. To find number 2,987, we refer first to the main guide number 29, then to the guide numbered 8—in the section between 29 and 30—and then to the number 7 tab next following. As there are never more than one thousand cards in a tray, any number can be found more quickly than in a bound book. If a card is misplaced in filing, the unit tab will greatly assist in locating the missing card. Suppose card No. 964 is missing; a search through the row of No. 4 tabs will locate it, no matter where filed. With this system of filing, a separate index by name is required, and this also is made on cards. For a very large ledger the numerical system is more frequently adopted than the alphabetical. [Illustration: Fig. 21 _c._ Balance Form of Ledger Card ] It is claimed that the numerical tab scheme affords one safeguard not found in an alphabetical system. A missing card is at once detected by the break in the row of tabs, but to make the safeguard of value it is necessary to leave the cards in the file even after accounts are closed.