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The zoom slider will only be displayed if the Map.MinimumResolution and Map.MaximumResolution resolution on the Map control have been defined. If a ESRI.ArcGIS.Client.TiledMapServiceLayer is present in the Map's layer collection, in most cases the minimum and maximum resolution will be set for you. If a Map only contains ESRI.ArcGIS.Client.DynamicLayer, you must set the minimum and maximum resolution explicitly.
The zoom slider will only be displayed if the Map.MinimumResolution and Map.MaximumResolution resolution on the Map control have been defined. If a ESRI.ArcGIS.Client.TiledMapServiceLayer is present in the Map's layer collection, in most cases the minimum and maximum resolution will be set for you. If a Map only contains ESRI.ArcGIS.Client.DynamicLayer, you must set the minimum and maximum resolution explicitly.