A manual (1) comprising a binder (6) and pages (3) releasably retained in the binder (6) comprises apparatus (2) for identifying an opened page (3) and for transmitting the identity of the page (3) to a computer (4). The apparatus (2) comprises a carrier member (15) which carries a plurality of photo sensors (16) for reading a binary identity code (17) along an edge of each page (3) for identifying the page. A plurality of input keys (37) on the carrier member (15) carry identifying symbols (40) which correspond to identifying symbols (41) provided on the pages (3) adjacent passages of text for facilitating inputting of select signals for operating the computer (4) to display additional data on a visual display unit (5) relating to the passage identified by the corresponding identifying symbol. A microprocessor in the carrier member (15) reads signals from the photo sensors (16) and the input keys (37) for identifying an open page (3) of the manual (1) and for identifying the passage for which additional data is to be displayed on the visual display unit (5). The microprocessor transmits a signal through a radio transmitter in the carrier member (15) to a radio receiver (35) of the computer (4), and the computer (4) is operated to display the additional data. The additional data which corresponds to the manual (1) is typically provided on a CD-ROM and is read into and stored in the computer (4). The apparatus (2) permits ready display of additional data relating to subject matter of a passage of text in the manual (1).