At this website, it says "Many OP-AMPs have two pins labeled OFFSET NULL. When both inputs are connected to the same voltage, the output should be zero. If the project requires a zero output under these conditions, the OFFSET NULL should be adjusted by adding a 10k pot between the Offset Null pins with the centre of the pot connected to 0v. By adjusting the pot, the output will produce 0v." And it gives this diagram. I am trying to duplicate this. I am using an LM741CN with a dual power supply (two 9V batteries,) but I cannot get 0V out. When I adjust the pot with the wiper connected to -V, the voltage changes and even goes from positive to negative, but the change is so abrupt that it is impossible to stop at 0V. I see in the diagram that the center of the pot is connected to -V instead of 0V, and I have tried it both ways. Which is correct, and what could I be doing wrong? Thanks.