Main Page | See live article | Alphabetical index A redundancy check is extra symbols added to a message for the purposes of error detection or error correction. A check digit is a digit used as a redundancy check. The UPC barcode has a check digit computed by multiplying digits by alternately 3 and 1 and adding them up. For instance: 070617006092 0+0+1+0+6+9 =6 7+6+7+0+0+2=2 3*6+2=0, so the check digit, which is the 2 at the end, is correct. A longitudinal redundancy check is computed by exclusive-oring all the bytes in a message. See also: Cyclic redundancy check. This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.