MODEL RELEASED. Gearbox research. Technician testing an engine gearbox (green) using holographic interferometry as part of a development programme. This non-destructive test shows the change in shape of the gearbox casing during operation. A laser beam is shone through a reference hologram of the gearbox and onto the gearbox itself. The areas of derformation appear as a series of dark lines (an interference pattern). The pattern can be recorded and analysed to determine the amount of deformation. Photographed in Germany.