Resistance and Ambient Temperature criteria goes hand in hand, in order to determine the rated resistance at 25ºC. Since 2.0 Ohms is the minimum resistance required, the designer must calculate what resistance is at 25ºC is needed to satisfy this requirement at 50ºC since the operating/ambient temperature is 10ºC to 50ºC. R50 / R25 = 0.454 , R10 / R25 = 1.70 (Ametherm R/T Curves data) so 2.0 / 0.454 = 4.40 Ohms is required at 25ºC. Ametherm Thermistor that is suitable for this application will be rated for: 5.0 Ohms at 25ºC, since the closest rating that is above 4.4 Ohms is 5 Ohms. At 10ºC= 5.0 * 1.70 = 8.5 Ohms, meeting the minimum resistance requirement.