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(EDAC, or "error checking andcorrection", ECC) A collection of methods to detect errors intransmitted or stored data and to correct them. This is donein many ways, all of them involving some form of coding. Thesimplest form of error detection is a single added paritybit or a cyclic redundancy check. Multiple parity bits cannot only detect that an error has occurred, but also whichbits have been inverted, and should therefore be re-invertedto restore the original data. The more extra bits are added,the greater the chance that multiple errors will be detectableand correctable.Several codes can perform Single Error Correction, DoubleError Detection (SECDEC). One of the most commonly used isthe Hamming code.At the other technological extreme, cuniform texts from about1500 B.C. which recorded the dates when Venus was visible,were examined on the basis of contained redundancies (thedates of appearance and disappearance were suplemented by thelength of time of visibility) and "the worst data set everseen" by [Huber, Zurich] was corrected.RAM which includes EDAC circuits is known as errorcorrecting memory (ECM).[Wakerly, "Error Detecting Codes", North Holland 1978].[Hamming, "Coding and Information Theory", 2nd Ed, PrenticeHall 1986].