The custom function below counts the unique values only from a given range. This function uses the fact that a collection can only hold items with unique identifications keys. If you try to add an item with a key that already exists in the collection, an error will occur.

Function CountUniqueValues(InputRange As Range) As Long
Dim cl As Range, UniqueValues As New Collection
    Application.Volatile
    On Error Resume Next ' ignore any errors
    For Each cl In InputRange
        UniqueValues.Add cl.Value, CStr(cl.Value) ' add the unique item
    Next cl
    On Error GoTo 0
    CountUniqueValues = UniqueValues.Count
End Function