////Hey ,Hey then why Erik is playing with lookup table when I specifically ask for SHT11 .Erik do ya wanna *confuse* me

George,

nobody wants to confuse you! All people here are spending their costly time and energy and want to help you. But you don't want to read, you don't want to understand and instead of this you insult us and call our well meant recommendations to be 'oversmart'.
Know you what? Trying to help you is a challenge! You don't have the simplest idea of how a look-up table works. Why haven't you had already a search by google about 'look-up tables', 'calibrations', 'linearizations', and such stuff? Instead of this you are accusing us to confuse you. Erik has worked on look-up tables at a time you weren't even borne. So, why do you think he is 'playing' with look-up table and want to confuse you? Why aren't you thinking that YOU could probably be the reason for all this confuse?

Last try:

You buy a temperature sensor. From datasheet you see, that error at 25.0°C can be +-1°C. So, when actually having 25.0°C YOUR individual sensor can give you the following results: 24°....26°C. Ok? (We know it very surely, that actual temperature is 25.0°C, because we have tested it by the help of another temperature sensor, which is guaranteed to be extremely precise!!!)
Now we want to have a look at actual reading of YOUR sensor: AT 25.0°C it gives you 25.7°C. Ok? Real temperature IS 25.0°C, but your sensor tells you it is 25.7°C. Ok?

Now we put the sensor away, go shopping, eating, sleeping, anything you like. Next day, we take YOUR sensor again. And because God is good to us, we will again have a temperature of exactly 25.0°C. What will YOUR sensor give you NOW? 24°C?, 197°C?, -2578.9°C? You can tell me, when having a look into datasheet. Look how 'repeatibility error' is specified. And if 'repeatibility error' is +-0.1°C, then YOUR sensor will give you 25.6°C...25.8°C!!!
Whenever you take YOUR sensor and real temperature to be measured is 25.0°C, then YOUR sensor will give you a reading of 25.6°C....25.8°C.

Now assume a friend of you will also buy the same sensor type. What reading will HIS sensor give, when having 25.0°C? You can tell me from datasheet: Something between 24°C...26°.
Now we want to have a look at actual reading of HIS sensor: AT 25.0°C it gives him 24.6°C. Ok? Real temperature IS 25.0°C, but HIS sensor tells him it is 24.6°C. Ok?

Now we put the sensor away, go shopping, eating, sleeping, anything you like. Next day, we take HIS sensor again. And because God again is good to us, we will again have a temperature of exatcly 25.0°C. What will HIS sensor give him NOW? 24°C?, 197°C?, -2578.9°C? You can tell me, when having a look into datasheet. Look how 'repeatibility error' is specified. And if 'repeatibility error' is +-0.1°C, then HIS sensor will give him 24.5°C...24.7°C!!!
Whenever he takes HIS sensor and real temperature to be measured is 25.0°C, then HIS sensor will give him a reading of 24.5°C....24.7°C.

Now, look-up table comes into play.
You want to make your sensor to give a reading, which is as precise as possible. So, you must correct reading of sensor in some way. How?
For temperature of 25.0°C you know how to correct error: Because YOUR sensor gives you a reading of 25.6°C...25.8°C, means 25.7°C +-0.1°C, entry of look-up table must be '-0.7°C'. Got it?

Means, if YOUR sensor output is 25.7°C, microcontroller put his eyes into look-up table and must find '-0.7°C'. This means, that output of sensor must be subtracted by 0.7°C, when sensor reading is 25.7°C. So, whenever YOUR sensor gives a reading of 25.7°C, microcontroller makes a correction by subtracting 0.7°C (adding of -0.7°C).

Now, how would look-up table of your friend's application look like? Would he also find '-0.7°C' in his look-up table? NO! Because HIS sensor gives him a reading of 24.6°C, in his look-up table he must find '+0.4°C'. So, whenever HIS sensor gives him a reading of 24.6°C, microcontroller makes a correction by adding 0.4°C. While YOUR microcontroller has to add -0.7°, HIS microcontroller has to add +0.4°C.

Consequently, for every sensor output there should be an entry in look-up table. But Erik has shown you a way, how you can minimize size of look-up table. But instead to thank him, you accused him to confuse you...

How to create a look-up table? YOU must create it! And you must use a very very precise reference temperature sensor, which tells you, which actual temperature is. Take sensor output for a few different temperatures and create a scheme like Erik told you.
Of course, you can create look-up table by other methodes. E.g. concept of reference points and piece-wise linear interpolation. But that's a different story.

Kai