There may be times when you will wish to keep together all correspondence pertaining to a given subject--as a contract in which you are interested. A folder can be made for this contract, headed with the subject name, and filed in its proper place in the alphabetical index. Cross-reference cards can be made, headed with the names of individuals, and referring to the subject. Perhaps, when the contract is completed, there will be no further reason for keeping the correspondence together, and it can then be distributed according to the regular alphabetical arrangement. Should you wish to adapt the geographical idea to any part of the correspondence, the alphabetical index lends itself to the change without disturbing the general arrangement of the files. It can be expanded to any size; any class of correspondence can be segregated; and with properly subdivided indexes, papers can be quickly located. Probably the two most important advantages of the alphabetical over the numerical system of indexing are its economy of operation and safety. As to the first named advantage, there is a saving at the start in the outfit required. Only the letter file and alphabetical index are needed--there is no investment in a card-index outfit, unless it be a very small one for cross-references. But the greatest saving is in the time required for its operation. Without considering the operations involved in filing letters, compare the two methods when a letter is wanted from the files. Suppose that the file clerk has received a requisition for the correspondence of the Norton Machine Company. With the numerical index, the following steps are taken: (1) Open card index drawer; (2) Refer to cards filed back of the N guide, and find index card showing that folder _No. 610_ holds the correspondence; (3) Close card index drawer; (4) Open vertical file drawer; (5) Refer to folders back of the _600_ index, find _No. 610_, remove folder; (6) Close vertical file drawer. When the alphabetical index is used, only the following steps are necessary: (1) Open vertical file drawer; (2) Refer direct to folder of Norton Machine Company, back of the _N_ guide, and remove correspondence; (3) Close file drawer. [Illustration: Fig. 22. Alphabetical vs. Numerical Filing] This is merely an application of the principle that a straight line is the shortest distance between two points, as illustrated in Fig. 22. Alphabetical indexing is the safer for the reason that there is less liability of filing a letter in the wrong place. With the numerical system, the filing of letters in the wrong folder is not uncommon, and when this is done the letters are practically lost.