the invention requires the removal of the photographic plate from leak locator system 10 for purposes of developing the first reference image the plate is then returned to its original position in leak locator system 10 this step of removing and returning the photographic plate image recording medium 32 effects another result useful to the practice of the invention in that it causes the photographic plate to be displaced to at least a minute degree from its original position from whence the first reference holographic image was produced this slight displacement of the plate causes the second holographic image to produce patterns of interference in the background field when the second holographic image is superimposed over the first fig2 shows a representative example of an image achieved using a leak detector constructed in accordance with the present invention shown therein is an outline of a closed flute 56 wherefrom no simulated leakage flow emanates and an outline of a second flute 58 which is opened slightly at locale 60 for allowing such a flow to escape generally the dark bands 62 and the illuminated bands 64 over the background field of fig2 portray the characteristics of the interference to be expected on recording medium 32 after the second holographic image is superimposed upon the first at designation 66 there appears a disturbance in the otherwise uniform pattern created by bands 62 and 64 which disturbance correlates with.