Nyquist C4000 Series System Software - Queued Zone Paging/Page Stacking License. Queued Zone Paging / Page Stacking is disabled by default on every C4000 system. In addition to allowing multiple users to simultaneously page to the same zone or zones (e.g., in airport terminals, etc.), Queued Zone Paging is an effective way to eliminate feedback in areas where a paging device (e.g., phone, microphone, etc.) may be in close proximity to speakers receiving the page. Installing this license enables Queued Zone Paging / Page Stacking on the system and allows the user to create one (1) page stacking queue. Each NQ-C4000QPL license key installed/added to a system incrementally increases the page stacking queue limit by 1. For example, installing three (3) NQ-C4000QPL licenses will permit up to three (3) page stacking queues to be created on a system.