In an improved approach to mounting optical elements in a fiber optic device, the positioning and orientation of the element are more accurate and the temperature dependent variations of the position and orientation are reduced. The device includes multiple chambers in fluid communication with one another. The at least one attribute is sensed by the sensor or derived from signal output by the sensor. Novel nucleotide sequences, assays and primers are disclosed for the methods of the invention. The first support wall is positioned adjacent the rear wall and the second support wall is positioned adjacent the side wall, and with the feet resting on the standard refrigerator shelf.