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(1) Do not start to make a new class or revise an old one with preconceived fixed notions respecting its scope and the particular subdivisions required. Wait until all patents pertinent to the subject have been seen and adequate knowledge of them acquired. In other words, make no a priori classification but discover and assemble all the facts and from them make your inductions. Then the common characteristics of the subject-matter of the class may be intelligently defined, the limitations of the class marked out, and its relation to other classes set forth. Bear in mind that the Patent Office classification deals with the subject-matter of the useful arts rather than merely with existing classes, and that it is not therefore essential to retain classes that are found to be composed of unrelated or too distantly related units.

Assuming that the work of reclassification is undertaken by examiners who are already experienced in the subject-matter to be classified, procedure as follows is recommended:

(2) Utilizing your previously acquired knowledge of the patents in the class you are about to revise, subdivide the existing subclasses into bundles, so as to assemble in each bundle those patents deemed to have the closest resemblance to each other. For the purpose of this assemblage, consider each patent as an entirety and not with reference to various more or less important parts of that entirety.

Example: An apparatus comprising in alleged combination a means for decanting water, a means for electrolytically depositing impurities, and a means for filtering the water, should not be classified either as a decanter, an electrolytic apparatus, or a filter, but should be classified as a combination apparatus (taking it to the general art of liquid purification). So also the combination of a rotary printing-press with a folding mechanism, and a wrapping mechanism, should not be classified merely as a rotary printing-press, a folding machine, or a wrapping machine, but should be classified as a combination of the several mechanisms as an entirety whose functions carried out in proper order produce a printed and wrapped newspaper.

(3) Write an approximate or tentative definition of the matter thus assembled in each bundle and attach it to its appropriate bundle.

(4) Where it appears that the subject matter of any bundle formed from the patents of any subclass is analogous to matter in other subclasses of the same class or in other classes, a note should be added to that effect so that this matter may be given special consideration.

(5) When the same examiner or different examiners are working on different subclasses containing analogous matter, parallel lines of subdivision should be followed wherever possible, in order to effect an arrangement that will facilitate comparisons.

(6) When subdividing a group of more or less complex organized structures or mechanisms, note should be taken of subcombinations that form or it is thought should form the basis of other subclasses, either in the same or different classes, into which those details may be collected, either classified therein originally or by cross-reference.

Example: Assuming that the combination of press, folder, and wrapping mechanism, referred to in a preceding paragraph is to be classified in a class of Printing, on the entirety as a combination having the function of printing, plus other functions, and that folding and also wrapping are separately classified, then the particular type of press should be selected to be cross-referenced into a press-type subclass of the class of Printing, such as “Presses, rotary,” while the folding mechanism and the wrapping mechanism would be noted for cross-reference to other appropriate classes. Also, any part of the printing press, such as the inking mechanism, specifically described, should be noted for cross-reference into a subclass of Printing designed to receive the inking mechanism as a part of the printing press.

(7) After a knowledge of the material of the class has been obtained by estimating the resemblances between the individual patents that have been assembled in the several groups, comparison of these groups, represented by the bundles of photolithographs, by the aid of the approximate definitions and notes attached can be made. It can then be decided whether all of these groups are to be retained in the proposed class, and the retained groups can be organized into a class with the subclasses arranged so as to bring those subclasses having the strongest resemblances in closest relation, and in such order as to comply with the conventions adopted in the official classification. It will probably be necessary to have one subclass or group as broad as the definition of the class, to take unclassifiable matter and to provide for possible future inventions.

(8) Up to this point, more or less cursory attention may be given individual patents; but when an arrangement of subclasses shall have been tentatively adopted it will be necessary to consider each patent carefully to ascertain whether it is properly placed.

(9) Patents that, considered as an entirety, cover means not peculiar to the class or subject-matter being revised, should, in general, when assembled in groups as indicated, have a note attached indicating not only want of limitation to the subject-matter of the class but also a more appropriate class to receive them if such there be. Although a very large proportion of patents can be accurately classified as indicated by their titles and stated uses, the mere fact that in a patent found in a class the invention is called in the specification or claims by a name peculiar to the class is not of itself a reason for considering it peculiar to the class. A gas and liquid contact apparatus may be called a heater, a cooler, a gas-washer, a water-carbonator, a condenser, a disinfecter, an air-moistener, and so on, depending upon accident of use. If there are not elements in some claim to confine the means described distinctively to what it is called, or if there are no functions necessarily implied in the means claimed peculiar to the named use, the patent should not be kept in the class unless there is no other class in the office that can receive it.

Example: Where the matter claimed is a metal beam of peculiar cross-section, it should be classified with other metal beams, as in Class 189, Metallic Building Structures, even if it is named in the application as a beam of particular use, as a railroad-tie, car-sill, bridge-tie, etc. Should a mere dash-pot be found classified in Class 171, Electricity, Generation, a note should be attached indicating that it belongs in the appropriate element class.

(10) In giving this final careful attention to the patents, each should also be scanned to see whether it contains matter that should be cross-referenced. A few lines obscurely located in a specification may contain a disclosure of a most valuable invention. No class can be deemed complete until the disclosures appropriate to it found as parts of more complex inventions in other classes, or disclosures of analogous matter in other classes, are either cross-referenced into it or cross search-notes made.

(11) To indicate cross-references, from one subclass to another within the class or from the class under consideration into another class, attach a small slip of paper to the patent and mark on the slip the subclass number in which the cross-reference shall be mounted. If the matter to be cross-referenced relates only to a portion of a voluminous patent, the portion of the specification and drawing to be cross-referenced should be indicated. If the cross-reference falls outside the class, the class number should be noted in addition to the subclass number.

(12) Should it be found that the handling of copies in making examinations detaches the cross-reference slips, it may be advisable to mark lightly but legibly in pencil on the lower right-hand corner of the examiner’s photolithograph the number of the subclass or subclasses into which it is to be cross-referenced, or the number of the class and subclass in case it is to be cross-referenced to another class.

(13) Whether cross-reference notations are written on a separate slip or on the photolithograph, the number of the class and subclass into which a patent is to be cross-referenced should always be preceded by X (thus X 101-23) in order to distinguish the original classification notation from the cross-reference notation and enable sorting and indexing to be done without confusion.

(14) To indicate cross-references from other classes into the one being reclassified, set down the number of the patent in a notebook, placing after the number (1) the class and subclass in which it is classified; and (2) the number of the class and subclass in which it is to be cross-referenced.

(15) Should new subclasses be formed or transfers of patents be determined on, and lists of the patents, instead of copies thereof, be furnished clerks for the purpose of making such subclasses and transfers and correcting the official indexes and other records, each patent should be listed by number in column to the left of a sheet of paper or notebook, and opposite each patent number on the same sheet should be written (1) the number of the class and subclass in which it is officially classified; (2) the number of the class and subclass to which it is intended to transfer it; and (3) the numbers of the classes and subclasses, preceded by X, into which it is intended to cross-reference it.