Here is an excerpt from the GRE Knowledge Base that compliments what Don has posted. GRE makes the PRO-106 for RadioShack.
The excerpt begins saying "Your PSR-500/600 does not work like this". The PSR-500 is the GRE version of the RadioShack PRO-106. The word "this" is referring to a previous paragraph in the Knowledge Base article that describes scanning fixed conventional memory (as opposed to the Object memory architecture of the PRO-106).
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Your PSR-500/600 does not work like this. It does not process Scan Lists sequentially when scanning. Rather, it uses Scan Lists to organize your Scannable Objects into logical groups of your choosing. We call this "mapping objects to Scan Lists".
Scan Lists make it easy for you to find your objects, and make it easy for you to enable and disable groups of objects when scanning. The objects aren't really stored "in" Scan Lists. Rather, they are "members of" one or more Scan Lists that you have identified in the Scan List mapping for each individual object.
Once scanning begins, the radio doesn't know what Scan List(s) an object is a member of. It just knows that an object it is scanning is mapped to one or more enabled Scan Lists, and is not locked out. In this way it is possible to have objects that are mapped to multiple Scan Lists, without having separate and independent "copies" of an object for each Scan List that you want it to appear in, making memory usage much more efficient, and making scanning more effective, since the same object is not checked multiple times during a single scan cycle.
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To see the full article, go to the customer support section of the GRE America web site and look for the Knowledge Base article titled "Why doesn’t my PSR-500/600 stop in the current Scan List when I press the “MAN” button after the Scanner stops on an active Object?".