A method of controlling the effective impedance of a low-impedance high-temperature superconducting cable. The measured values are used in solving the equation of heat conduction to estimate the temperature of an internal body position. The test instruments are connected to form a communication ring. Some embodiments further display progress bars for one or more active applications. In one embodiment, the context controller includes: an event recorder that records occurrences of predetermined events and an event acknowledger, associated with the event recorder, that acknowledges ones of the events based on an identity of a currently-active context. This makes a flash ROM with a large erase unit compatible with a file system.