Sorry! I tried to give this answer a good rating... But I think I did it wrong.
This answer was a to-the-point, practical, way of going about it. (Without a lot of theory, which can put off some folks that "Just want to jump in and do it") I would only change one thing... I would add that one could also simply use a low value, linear taper pot to arrive at the proper resistance much easier and more quickly. Once the pot is set, just measure with meter what it's set at, and bingo, you have your answer! Just pick the nearest 'standard' value resistor out of the 'ole junkbox. (If, say, the pot indicated that 325 OHMS was ideal, use a real world resistor of 330 ohms... It will be close enough for the real world... remember, even a 5% unit will vary by 330 +-5%=16.5 ohms, more OR less than 330, or 313.5 ohms to 346.5 ohms. If you really want or need to be more precise, keep the pot, or buy 1% resistors.)
Junkman