A corner mounted tray, atop the upper surfaces of shower bath walls, is triangular in shape, comprises a perforated bottom surface, upstanding sidewalls and angled front wall and is releasably attached to a vertical wall by screws. The method for observing a fluid includes capturing an image of inorganic particles in a fluid for flow observation by irradiating the fluid for flow observation passing through a flow channel with light, the fluid for flow observation containing inorganic particles to be observed each having a planar surface, a dispersion medium to be observed, and a viscosity modifier. The table is installed on the frame to have the substrate to be mounted thereon. The effects that appear during the creation of the photograph comprising the surface to be scanned and that have a detrimental effect on the image, for example geometric distortion, lack of focus, blurring, shadows andor light reflection effects, digital noise, lack of contrast andor colorimetric shift, are removed or compensated. By monitoring the patient’s AV delay under these circumstances, useful information is obtained that can be correlated to other patient conditions or symptoms. An inclined portion facing a center shaft of the photoreceptive drum is provided at a leading end of the guide portion so that the gap maintenance member closely contacts the photoreceptive drum while pressing the photoreceptive drum in a radial direction of the photoreceptive drum.