A system that is suitable for extracting plasma from blood received from a blood supply is provided. A plurality of conductive elements are formed on the substrate. This absolute difference area changes periodically each time the dimension of the structure to be measured changes by \u03bb4, making it possible to determine the dimension of the structure to be measured based on that change. The LED is positioned so as to direct most of its light at an angle which would allow the illumination of a document held in the device bearing hand and allow the LED to be shielded by the opposing hand. In one embodiment, a wireless receiver includes signal tracking and timing logic to facilitate the timing of a demodulation operation such that the demodulation operation occurs on the proper symbol boundary, particularly when the OFDM signal has multipath components and the second component has greater power than the first.