Abstract: A detector for detecting edge cracks in the web in a papermaking machine includes a plurality of light sources for directing light at the web and a plurality of light sensors for receiving the light through the cracks for generating a plurality of signals indicative of the dimensions and shape of the crack. The size and shape of the cracks are determined from the sensor outputs by a processor and preferably displayed on a suitable display. Crack shapes are determined by introducing a delay parameter which relates the output for each detector channel to the time a first detector channel is triggered. In particular, the first detector channel which is triggered is given a delay value of zero, while other channels are given delay values greater than zero depending on the order of activation. The signal acquisition and analysis are designed to be compatible with a personal computer so as to ensure the system's portability.