=242.= In classification systems in which the class numbers are used for charging and all other purposes it is necessary to provide a series of elaborate auxiliary marks to distinguish book from book in the same subdivision. Thus, in the Decimal scheme, 621·18 is the number for books on boilers. If there are six books on this topic, some distinction must be used in charging to enable the librarian to know which book has been issued. Mr Cutter has devised a table for this purpose, which is known as the “Cutter Author Marks,” by which surnames are arranged according to their initials and qualified by a number thus: Abbott = Ab2. Acland = Ac6. Cook = C77. Cousin = C83. Crabb = C84. Gardiner = G16. Gerry = G36. Gilman = G42. Shock = Sh8. The six books on boilers would accordingly be distinguished by receiving these author marks, and the numbers might become: 621·18 Ab2 Abbott on Boilers. 621·18 C83 Cousin „ 621·18 G16 Gardiner „ 621·18 Sh8 Shock „ In the Subject Classification these books when given the number for boilers, C210, could be further distinguished by the numbers of the biographical tables, thus: C210 ---- Abbott on Boilers. 3011 C210 ---- Cousin „ 3669 C210 ---- Gardiner „ 4565 C210 ---- Shock „ 7863 =243. Book and Shelf Marking.=--It is better to have the class numbers stamped on the back of the book at once than to rely on tags or labels, which have a tendency to peel off. In some open access libraries using ordinary gilt lettering, a subsidiary marking has been adopted to prevent misplacement and to aid replacement.