I have the same gauge as dragman64, and it works relatively well. It responds instantly to any bog or hesitation, you can just glance at the gauge and tell if it's a rich or lean condition. But for fine-tuning the engine if it already runs well, it's not quite as useful. I tried to adjust my jetting to get the gauge to read 14.7:1 (halfway lit up) while cruising, but no matter how much I leaned it out, it still ran 1 or 2 bars rich, clear to the point that I could tell it wasn't running as well. Each engine is different, and I think the only way to really fine-tune is by feel. But when trying to diagnose a bog or bad running condition it's a pretty handy tool.