In computing, the process of checking that data being input to a computer have been accurately copied from a source document.
This may be done visually, by checking the original copy of the data against the copy shown on the VDT screen. A more thorough method is to enter the data twice, using two different keyboard operators, and then to check the two sets of input copies against each other. The checking is normally carried out by the computer itself, any differences between the two copies being reported for correction by one of the the keyboard operators.
Where large quantities of data have to be input, a separate machine called a verifier may be used to prepare fully verified tapes or discs for direct input to the main computer.