I am having a hard time figuring out why i need a 2nd resistor to measure resistance from a thermosister. ok so if we change the resistance of a 12 volt supply we end up varying the current. so in order to read it as volts we need to ad a resistor co the change we get is in volts not in current. how does this happen though, i can not see why adding a resistor of known value in series will now make the voltage vary instead of the current.....

Wow i think i just figured it out..... please tell me if i am right, what we are doing is trying to make a tempature sensor, we will start with a supply voltage of 3 volts then in to the thermosister witch will change the resistance according to tempature and as a result we will see on the trailing end of the thermosister a change in current while still providing 12volts since they are all independent of each other v=I*C if v is constant and we change I then c must change also. so in order to measure the resistance of the thermosister that is now supplied with a varying current and a constant resistance witch results in a varying of the voltage.