I made the closed loop monitor. I had it on my 1996 Tercel (same engine as my Paseo) for a couple months. After hooking up the
scangauge I noticed a huge difference in readings. Its possible I had the closed loop monitor tuned wrong, but the two showed vastly different readings.
The air/fuel ratio meter you can buy from autozone or your local parts store for $20. The bought gauge will look better, save you a hassle, and probably cost only a tiny bit more.