Thanks to MikMo for the indication on relation between distance and precision. In choosing criteria for Sensors I will check this 
I would like to know something more about aim7100 work. If I got it properly, you use several sensors (4 + 3 ?) connected through an ethernet wire with 4 strings and two of them are not used right now. Do you think would it be possible to use them for other variables (let's say "light" or "humidity" for instance?)
Eprom and SD card are used to store data that you can download to your PC and analyze. Is that right?
The choice to have several sensors is related to the need of making an average of the temperature detected?
For all of those who will kindly help me, sorry if those questions will sound banal to you, I am still in the stage of learning as much as I can on the possibilities of Arduino for environmental variables monitoring purposes. In the meantime I am practising with Arduino "Getting started" and "Experiments" 