Any unit (like the the Holley meter, the old Halmeter, the Cyberdyne, J&S's unit, etc) that is based on an everyday 02 sensor rather than a true wideband air/fuel meter and sensor, will confound and confuse you rather than give you data. There are now a number of true wideband air/fuel meter packages out there. The Dynojet Commander and the Innovate are two that come to mind, I believe they're under $400, and have lots of neat features way above and beyond just being a meter. Check 'em out.
Hope this helps,
Chris Weisberg
Carroll Shelby Enterprises
(310) 538-2914