Abstract: Apparatus for and a method of marking a web 10 advancing along a path includes a monitoring station 11 at which the web 10 is observed and including a signal generator arranged to produce an appropriate mark signal on detecting a location to be marked as well as the nature of the required mark. A tab applicator 20 is disposed downstream of the monitoring station for applying an adhesive tab 34 to the web in a timed relationship to the advancement of the web so as to adhere the tab 34 to the required location on the web. The tab applicator includes an online printer receiving a signal from the signal generator, whereby an applied tab may carry appropriate indicia for the location being marked.