A floating bath assembly in which the user gets into an open tank in which he rests floating in a slightly heated high-density saline solution in a decubitus dorsal position. Each of the sensor rows detects the light emanating from the sheet material in a certain spectral channel. The stream held in the first buffer is written on the recording medium. This water reservoir is connected to the suction line via an inflow line. A heating or tempering unit for the lower measuring part is arranged below the lower measuring part. An intermediate portion of the valve is in facing engagement with the collar deck, and an annular wall portion of the valve extends from the inner end of the intermediate portion.