Reference sources are research tools that can provide answers to specific questions, such as brief facts, statistics, and technical instructions, background information, or direct information seekers to additional information sources. Reference sources are designed to be consulted rather than being critically read. Their design is generally dependent on the type of information and treatment provided. Reference materials can be arranged alphabetically, topically or chronologically. Many of them contain cross listed information and more than one index. Where users are not sure which reference tool is best suited to their information need, a reference librarian will be able to assist them. Reference sources are not circulated, they are located in a separate reference collection in the reference section. This practice makes reference sources readily available and easily accessible. There are thousands of reference sources available that cover practically every subject. Although the term reference "book" is frequently used, reference sources can be books, serials, on-line databases or Internet resources.