Apparatus for printing data on a document includes two printing devices. The first printing device 42 prints the data in human readable form on a document. The second printing device 52 also prints the data on the document in a form which can be read by an optical reading system.
The first printing device operates in response to data signals supplied to the apparatus, from a keyboard 32 or otherwise, to print on one portion of the document. Simultaneously coded representations of the data being printed are produced and stored.
The second printing device operates in response to the coded representation of the data and prints further representations of the data on another portion of the document. These representations can be read using an optical reading system.
The coded representations can include additional code providing for error correction.