A method for controlling fluid flow in an assay device that employs a membrane is provided. The imaging lens system includes two lens elements each made of a homogeneous material and having a positive optical power, and fulfills the following condition: 1. In some embodiments, the unit employs spring means for maintaining the required spatial relationship, which is maintaining the required distance between the indicia carrier on which the information to be displayed is contained, and the lenticular panel containing the lenses used to display the information. The first and second MUXs respectively receive results from the butterfly operator to output the results in an increment of N when receiving a control signal \u20180\u2019 from the controller, and respectively outputs different N data when receiving a control signal \u20181\u2019 from the controller. The sidewall panel may also be included in an assembled barrel cooler. The stem is sized and shaped for reception in a bone at the joint such that the tip of the stem is exposed to locations outside of the bone.