Abstract: A display device 10 consisting of five cells of seven segments each, is used in a photocopying machine in order to indicate normal operation and certain abnormal situations. The latter are indicated by means of messages in plain language, represented by cyclically moving characters. The messages are stored permanently in an EPROM 50, from which they are extracted as required under the command of a CPU 80 in relation to the corresponding type of abnormality, as detected by a set of sensors 82, 84, 86. A suitable subroutine causes the letters of message to slide along the cells of the display device 10 from right to left.