Devices and methods for performing assays on materials, particularly biological materials, are provided. The packet processing pipeline is configured to assign a virtual port from a plurality of virtual ports to a packet received via one of the physical ports, wherein a quantity of the virtual ports is larger than a quantity of the physical ports, and wherein, for each of at least some of the physical ports, multiple virtual ports correspond to one physical port. As a result, it is possible to suppress mask misalignment from occurring. The drive wheel is locked for rotation with the shaft by a set screw in a threaded bore extending into the wheel at an angle with the axis of rotation of the wheel, and with the nearest portion of the bore spaced from the axis of rotation to allow the threads of the set screw to cut into the surface of the rotating shaft. The terms n, m, and a are integers greater than one. The sensors may have diverse compositions.