[Illustration: FIG. 75.--Tier Marking of Books (Section 243).] [Illustration: FIG. 76.--Shelf Front with Class Divisions and Number (Section 244).] [Illustration: FIG. 77.--Tier Guide showing Construction (Section 244).] =244.= It is desirable that the arrangement of the shelves should be made as clear as possible to the staff and to readers by means of various guides, and these are particularly necessary in open access libraries. The best general guide is a plan of the department showing the disposition of the books in the cases, and indicating the sequence of the classification by means of arrows. The plan of the Croydon Central Lending Library may serve as an example. If the classes are indicated chromatically: for example, 000 red, 100 blue, 200 yellow, 300 green, etc., the plan will be more easily followed. Such a plan, drawn to a large scale, framed, and hung in a conspicuous position, will give readers a valuable conspectus of the department. +----------------------------------------+ | =CHART OF SUBJECTS | | IN THIS TIER= | +========================================+ | PHYSICS | | 535 LIGHT | +----------------------------------------+ | PHYSICS | | 536 HEAT | +----------------------------------------+ | PHYSICS | | 537 ELECTRICITY | | FOR ELECTRICAL ENGINEERING SEE 621·3 | +----------------------------------------+ | PHYSICS | | 537 ELECTRICITY | | 538 MAGNETISM | +----------------------------------------+ | PHYSICS | | 539 MOLECULAR PHYSICS | | 540 CHEMISTRY | | 541 THEORETICAL | +----------------------------------------+ | CHEMISTRY | | 542 PRACTICAL EXPERIMENTAL | +----------------------------------------+ FIG. 78.--Tier Guide showing Lettering of Front (Section 244).