Gene,
You ask a very good question and have received some excellent, experienced (Sovereign-user) answers from Rick, Mike and Adam.
Typically, the various Sovereign ID meters track the audio tone and meter output voltage and produce an ID reading that is in step with them. However, once the audio tones and ID meter voltages become weak, less stable and non-repeatable, accurate target ID becomes problematic and less accurate.
ID meter design does make a vast difference as to how good or bad the meter is able to 'handle' these types of weak responses. First, the ID meter's input sensitivity and 'signal conditioning' design plays a big part in being able to process weak signals and in producing an accurate ID indication. Also, ID meters that use 'computer chip' micro controllers -- such as the Target A.I.M. PRO -- have the added ability to 'intelligently' 'look' at and process a particular, or series of target or voltage readings, and make a determination based on its multi-faceted internal software program as to whether the target is good or bad and where to indicate the target on the display. This is, for example, what Tesoro does with their 'Sum' mode and White's with their DFX's 'Best Data' and 'Correlate' modes. Basically, these modes average and compare readings to determine the most accurate ID possible . We also (automatically) do something similar to this within our Patriot Target A.I.M. PRO ID meter.
Still, as Rick, Mike and Adam have said, you need to master certain Sovereign operational techniques to get the most out of any 'add on' ID meter used.
On the Target A.I.M. PRO meter, many deep, marginal targets will be indicated by the meter pointer 'spiking' up toward the correct ID reading or category. Usually, when you see these kinds of indications, it means that the target is deep and not producing enough signal to enable a 100% accurate meter or audio indication. These types of signals should always be retrieved no matter what the meter or audio ID indicates. Especially if they sound small and deep in the pinpoint mode too.
Climbing meter readings and audio tones are indicative of a good target deep in the ground and should always be carefully investigated.
Joe