The nominal 0 deg C voltage and the temperature coefficient are 
given in the datasheet with their respective tolerances. 
The nominal 0 deg C voltage is specified to be 986mV +/- 5% max 
error. So, the 0 deg C voltage of the temperature sensor can vary 
worst case almost +/- 50mV from device-to-device. This is roughly 
equivalent to +/- 14C. Note, that this variance is primarily 
device-to-device dependent, so that with proper calibration on an 
individual device, very accurate absolute temperature can be 
obtained with the full resolution of the ADC12.