What is the fine-grained topic of the following text: Exhaust-gas temperature gauges are susceptible to many sources of error due to the nature of the sensor-probe signals, which are very low voltage (in the order of millivolts), and since the temperature of the reference junction (typically where the probe connects to the gauge) needs to be accurately determined. Only return the topic.
Challenges and errors in exhaust-gas temperature gauges due to low voltage and temperature determination