ScanMaster II
Upon enter P.E. mode (Or is it over 3.0 TPS volts? I can’t remember), ScanMaster WILL record the highest KNR reading and the Lowest O2. By pressing both the recall and mode buttons at the same time, you will see the MPH where the previous readings were recorded. A great feature!
PLUS, monitoring all the other sensors is a big plus for SM. From money vs feature perspective, the ScanMaster gives you the best value.
---However----
The original question, I believe, was when you run BOTH (a SM and Knock gauge, where the SM isn't showing knock, but the gauge itself is) which one is telling the REAL story!
I don't run both, so I can't offer any confirmation that this is a normal or unusual deal. But that won't stop me from offering an opinion!
To be honest, the SM is only reporting what the ECM is adjusting for, not the actual knock reading. Also, the "Sample Rate" on the SM/ECM is way slower, so you may just be seeing knock SOONER on the gauge, and it may take a few frames before you see what action is being taken to reduce the knock. That may be your difference. The SM is not reporting the knock, but actions taken by the ECM to reduce it! The gauge is more "Real Time", so if you left your foot in it longer, SM readings would eventually correspond to those on the gauge... They would have to, since the same sensor is used.
In other words, you are attempting to compare Apples to Oranges. SM reports Degrees of timing reduction. Your gauge reports Knock Severity. They are RELATED, but are not the same units, and are not displayed at the same rate.