Recently developed high-quality thermistors are accurate, stable, and reliable. Within their operating range, commercially available thermistors will match a resistance-temperature curve within approximately 0.1°F (0.056°C). Some manufacturers of thermistors can supply them with a stability of 0.05°F (0.028°C) per year. For direct digital control (DDC) systems, the same sensor is used for both temperature indication, or monitor- ing, and temperature control. In DDC systems, RTDs with positive temperature coefficient are widely