-a DMM
-3-temrinal potentiometer (two end pins, one to GND, one to some voltage supply, center pin to the DMM)
-3-terminal linear voltage regulator
-two capacitors (one between input/ground and output/ground of regulator)
Doesn't realy matter what voltage the potentiometer max value is or the regulator voltage, as long as the pot isn't such a small resistance that too much current is flowing for either the pot or regulator. Of course, also make sure the regulator can handle the input voltage you give it (like from a wall wart or something). You might want to use 10V just so it's easier to work with the numbers (5V,12V also works)
Done!