The Steinhart-Hart formula is an excellent equation for computing the relationship between the resistance of an NTC thermistor and its body temperature. A simple program for computing the resistance versus temperature characteristics of any Littelfuse thermistor can be downloaded at the following link: http://www.littelfuse.com/products/temperature-sensors.aspx?utm_source=ussensor.com&utm_medium=redirect&utm_campaign=ussensor-lf. It is important that the data points entered into the equation (either 3 or 4) encompass the temperature range of interest and are selected to be equally spaced as possible. It is also essential that the data entered is taken from a valid thermistor resistance versus temperature table.