My point exactly. And the purpose of checking the devise using the Ling sounds is to insure that the devise is picking those sounds up appropriately. Only in that way can you be sure whether it is the devise malfunctioning, or the fact that the child cannot pick up those sounds at the current level.
And yes, it is necessary to change the sentence used for testing from time to time to insure that a child is responding to what they actually hear and not what they have come to expect to hear.
