Each book is assigned a unique and specific call number- a combination of letters and numbers that designate it by subject and then within subject. No two books or other materials have the same exact call number. Call numbers usually consist of 2 to 4 lines of letters and numbers and are found either on the spine or on the front lower left-hand corner if the spine is too narrow.
BUT… the tricky part of the 3rd line of the call number is that its numerical component is read as a decimal number.