Filming was done under true refining conditions through a 3 cm wide peep-hole into the gap of a LC double disk refiner, Beloit DD 24”, with a simultaneous injection of tracer particles and man-made fibres to facilitate the observation and analysis of the movements of the fibre/flocs. To obtain more information about what happens at the bar edge, one bar of the dummy was equipped with an embedded mirror, which gave a side view of the groove and the bar edge.