In one embodiment, an integrated circuit includes a self calibration unit configured to iterate a test on a logic circuit in the integrated circuit at respectively lower supply voltage magnitudes until the test fails. In one embodiment, a kit of superior or inferior prostheses is provided, in which the prostheses have at least two dimensions that vary among members of the kit independently of each other. The third rail can move together with the second rail when the latch member and the lock member are engaged, and the third rails can move freely by itself when the latch member and the lock member are disengaged.