What is the difference between call no and accession number?

Call Number: it reveals the exact location of a document in the library.  It is a unique number used for classifying the documents in a library to arrange in the library shelves according to its similarity in subject, author ....etc..

Accession number:

Sequential number assigned to each record or volume as it is added to a database (such as a library catalog or index) and which indicates the chronological order of its acquisition.

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these are the codes to identify the right book and its accessibility location of the book in a Library Management System. Thanks.

A call number is a unique code that has been assigned by a cataloguer to an item and that is affixed to both the inside and outside of the item. This number is used in the bibliographic record for that specific item, it identifies which copy it is (particularly when more than one copy of an identical book is present), and it indicates the relative location of the item on the shelf. Usually, a call number is created by using the classification number (from either the Library of Congress Classification System or the Dewey Decimal System) for the title, followed by additional information to indicate such things as publication date, volume number, copy number, and/or location symbol

An accession number, also known as a catalogue number, is a unique number given to each new item that is acquired by a library. The numbers are typically in sequential order, and aren't usually used more than once, even if an item is removed or replaced within the collection, regardless of whether or not there is already an identical copy of the item in the library's holdings. As such, an accession number is helpful in distinguishing multiple copies of the same book, as well as different volumes (or editions) of the same title

The call number refers to the Dewey Number on a book's spine label. That is the book's "address" on the shelves. An accession number is a number allocated to a specific copy of a book, for record keeping.

Call Number of a document i reveals  the exact location of a document in the library.  It is a unique number used for classifying the documents in a library to arrange  in the library shelves according to its similarity in subject (Mostly) , author ....etc..

Accession number is also a unique number allotted by the librarians to documents while adding to the library collection.  it is serially numbered. the last accession number will be the last document acquired by the library in its kind and last accession number will be total number of  documents available in its kind in the library.

Call Number mentioned the details of Subject wise position arrangement of books on racks. Accession number  allot the number by the librarian to books from first book to last book. Last Accession number mentioned total number of books in library. by example last book allotted by 25354. Total number of books available in library is 25354.

Call Number - a combination of classification number and author number assigned from the classification scheme followed by the library. Its unique and shows the location of the book on the shelves. It brings together similar subject collection on the shelves. Call number is normally printed on the book spine. 

Accession number is the simple sequence number to register each new book acquired in a library. It's assigned in an ascending order. The last accession number shows the total number of items available in the Library.

Traditional libraries maintain a register while others use electronic registration where numbers are generated automatically. Most of the libraries now use Barcodes as an alternate to the manual accession system.