A method for tracking a user’s gaze point using a mobile terminal is provided. Using an optical disc wherein ratios of error rates before and after an environmental test at 80 C. Each section of distinct width forms a transmission having a distinct characteristic impedance. The decoding apparatus uses a memory to store the data signal separated by the demultiplexer, and a CPU to analyze the data signal stored in the memory. The control circuit includes a first input connected to a first hardwired configuration bit, a second input connected to a second hardwired configuration bit, an output connected to one or more of the PLD’s configurable elements, and a select circuit to selectively connect either the first input or the second input to the output in response to a select signal. The optical subassembly includes a housing having a channel formed within the housing for placement of at least one extrusion of the chassis within the channel.