(EDAC, or "error checking and correction", ECC) A collection of methods to detect errors in transmitted or stored data and to correct them. This is done in many ways, all of them involving some form of coding. The simplest form of error detection is a single added parity bit or a cyclic redundancy check. Multiple parity bits can not only detect that an error has occurred, but also which bits have been inverted, and should therefore be re-inverted to restore the original data. The more extra bits are added, the greater the chance that multiple errors will be detectable and correctable. Several codes can perform Single Error Correction, Double Error Detection (SECDEC). One of the most commonly used is the Hamming code. At the other technological extreme, cuniform texts from about 1500 B.C. which recorded the dates when Venus was visible, were examined on the basis of contained redundancies (the dates of appearance and disappearance were suplemented by the length of time of visibility) and "the worst data set ever seen" by [Huber, Zurich] was corrected. RAM which includes EDAC circuits is known as error correcting memory (ECM).