The Zoom to Full Extent tool allows users to quickly re-size the map to its original default extent. It is important to note this is not the same as the "extent of all layers". Rather it is the default extent determined by the NRI administrators when designing the map service. The user can zoom in and out beyond these defaults at will.
To return the map to it original default extent:
Select Zoom to Full Extent from the Map Tools drop-down list.
The map will immediately be re-drawn without further input.