The TR-971 air flow indicator may be used to confirm air flow levels of the TR-600 series PAPR. The TR-971 is designed to enable testing at various elevations and temperatures within the operational range of the PAPR system.The TR 971 air flow indicator may be used to confirm air flow levels of the TR 600 series PAPR. The TR 971 is designed to enable testing at various elevations and temperatures within the operational range of the PAPR system. See the User Instructions for details regarding how to use the TR 971.