Mr. Reynolds, You neglect to provide some critical information: What flux chemistry are you using? OA, WSF, RA? The validity of Omegameter testing is closely tied to flux chemistry. A few days ago, Tim Crawford, EMPF, gave a good overview of the uses of ionic cleanliness testers (e.g. Omegameter) and some of the associated problems. Tim was the primary author of EMPF report RR0013 "An In-Depth Look At Ionic Cleanliness Testing". I highly recommend reading that report when you look for the answers you pose. The report summarizes that the instruments should only be used for their designed purpose, as a process monitoring tool. Not as an analytical instrument. It is critical that you understand the information that the Omegameter (or similar) is telling you. For this reason, our lab recommends that all such cleanliness monitoring be baselined, with a more analytical and sensitive method for measuring ionic cleanliness. We use ion chromatography per IPC-TM-650, method 2.3.28. IC will tell you specifically what ions you have present. You can then tell what an Omegameter reading of 4.0 means for your technology. This is a very complex issue and cannot be adequately covered in such a forum. If you, or anyone on technet, have questions regarding bulk ionic cleanliness testing vs. ion chromatography, please call myself (Doug Pauls) or Terry Munson at 317-457-8095. Doug Pauls Contamination Studies Laboratories.