Variable Voltage Regulators with + and - 12v input?

Hi,

I have put one of these together for an ATX power supply and have come across something that I might be getting wrong....

In mocking up the LM317 circuit in breadboard (standar one found everywhere on line and on the LM317 pages), I have got the thing metering -11v to +11v??? I am using one of the black ground wires of the PSU on the black side of the volt meter, but cant figure out why I am not just getting positive voltages??? Could the diode be faulty? Or is this in fact correct?

Any help appreciated...

Depends where you took "ground" for the regulator from. If you've taken it from -12V, that will do what you say.