The indexer will return the counter for the given counter name if it has been registered otherwise it will return null.
Namespace:  Microsoft.TeamFoundation.Framework.Server
Assembly:  Microsoft.TeamFoundation.Framework.Server (in Microsoft.TeamFoundation.Framework.Server.dll)
Syntax
'Declaration
Public ReadOnly Property Item ( _
    counterName As String, _
    instanceName As String _
) As TeamFoundationPerformanceCounter
public TeamFoundationPerformanceCounter this[
    string counterName,
    string instanceName
] { get; }
public:
property TeamFoundationPerformanceCounter^ Item[String^ counterName, String^ instanceName] {
    TeamFoundationPerformanceCounter^ get (String^ counterName, String^ instanceName);
}
member Item : 
        counterName:string * 
        instanceName:string -> TeamFoundationPerformanceCounter with get
JScript does not support indexed properties.
Parameters
- counterName
 Type: System.String
- instanceName
 Type: System.String
Property Value
Type: Microsoft.TeamFoundation.Framework.Server.TeamFoundationPerformanceCounter
The performance counter for this counter name and instance, or null if it hasn't been registered
.NET Framework Security
- Full trust for the immediate caller. This member cannot be used by partially trusted code. For more information, see Using Libraries from Partially Trusted Code.