Here is the chart from the link Miata posted. I can't wait to try this.

Voltage (O2 sensor reading on Torque) - Conversion to AFR

0.97V - 12.1:1 - Very Rich - Forced induction and nitrous. you might want to be around here.
0.88V - 12.7:1
0.78V - 13.2:1
0.69V - 13.8:1
0.59V - 14.4:1
0.49V - 14.9:1 - (Stoich- pretty close to 15:1, this is where NA motors should be at)
0.39V - 15.4:1
0.30V - 16.0:1
0.20V - 16.5:1
0.10V - 17.1:1 - Lean