The OPC Historian Test Client application can be used as a diagnostic tool to browse the OPC HDA servers and interactively read data. The test client can also be used as a development helper tool. The server can be browsed to get the items supported by the server and the item names can be copied into the code of a client being developed. The client uses the OPCHDA.NET client component for the server access. All OPC HDA 1.2 functions can be called interactively to check if the values are returned as expected. This may help determine if an unexpected behavior has to searched in the client being developed or somewhere else.