Dave, thanks for the tip, it seems like it is the right way to go! As it is the same sugestion that Jumper gave, maybe you both could help me with this: how can I obtain stable raw data? because the values keep going up and down usually +-2 ADC values. Itīs not good for comparing values...is there a way to solve this?

ScaleRobotics, very very nice your altimeter project. As I said, I am very new to programming and I am trying to learn. Let me ask you something, I set the internal osc to 4MHz, should I use 8? And I am using rs232 for recovering data, will it work at 8MHz?
I guess that 8MHz would make things easier for this case...

If itīs not asking too much, Iīll translate my code and post here, then you could give me some tips if you guys have some time...Because I must be doing something very wrong, the pic was supposed to make this kind of calculation flawlessly.

Thanks!!!