>0.05C? 0.5 is hard already. 0.05/40, that means 0.1% accuracy in T!
>
>What to calibrate? 3 phase water in 1 atm? to hard.

No, boiling point of water is inaccurate, as it is too hard to hold the 
pressure accurately. AFAIK all high accuracy accuracy standards use solid to 
liquid phase of various substances.

So to achieve calibration in the OPs range, my suggestion is ice at 0C, and 
gallium at 38.5C (check this one, I am going from memory). There may well be 
others nearer the outer ends of the range he wants to measure. 

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist