Class 2 and Class 3 dielectrics are specified differently using their three characters. Because Class 2 and Class 3 dielectrics are not as stable as Class 1, their capacitance change is given in percent and not ppm per degrees Celsius. The first character defines the minimum operating temperature. The second character defines the maximum temperature range. The third character defines the maximum change in capacitance over the entire operating temperature range. For example: X7R has an operating temperature of -55°C to 125°C with a maximum capacitance shift of plus or minus 15% over that operating temperature range.