I think the usual approach is to use a Wheatstone bridge and an op-amp
thanks it cleared the SOMETHING which i wanted to use ill pop back when i get cleared as of how to do it 
Another common method is to generate a stable voltage source via a small regulator chip or zener diode and use that to supply to the pot that is adjusted to the desired 'setpoint' value to use.
Thanks is it possible to shut down the whole thing when the battery deops below the Required voltage ?