MICR is a contraction of the term Magnetic Ink Character Recognition. Magnetic ink is used in automatic character recognition applications. MICR is comprised of only 14 characters, which are the numbers 0 through 9, as well as four other symbols that denote Amount, Dash, Transit, and On-Us. MICR is printed on documents using a special type of magnetic ink that can be easily read by check scanning equipment. The MICR standard also requires very specific placement on a document, so that characters can be properly read at high speed.
MICR is most commonly used to encode the bank routing number, account number, and check number along the bottom edge of a check, which are then read at high speed by the check scanning equipment used by national check clearing systems. MICR has been the standard method for encoding information on checks since 1958, when it was adopted by the American Bankers Association.
The use of magnetic ink makes it easy for machines to read information encoded on a document, even if the MICR has been overwritten, perhaps by an accounting stamp, initials, or a signature. Because of this capability, the read error rate is quite low on MICR-encoded documents, which is particularly important in the banking industry.
MICR is also designed to be readable by humans, so it is structured to match Arabic numbers.