Abstract: The present invention discloses a device for indicating inadmissible length deviations of a perforated web, preferably a formaliner-perforated paper web to be used for the production of forms, where the printing press comprises at least one working mechanism provided with rotating working elements such as a means for punching perforations in the web or possibly a printing unit and where a transmitter receives values corresponding to the velocity of rotation of the rotating working elements and converts the values into pulses, and where another transmitter receives values corresponding to the velocity of the web and converts those values into pulses. The device uses a measuring unit which receives the pulse information from the transmitters in order to continuously indicate and control the length of each length of perforated web during operation of the printing press. For each transmitter, the measuring unit comprises at least a primary counter and a secondary counter.