3M Versaflo TR-973 air flow indicator may be used to indicate air flow levels of the TR-600 and TR-800 series PAPRs when used with tight fitting face pieces. The TR-973 is designed to enable testing at various elevations and temperatures within the operational range of the PAPR system.3M Versaflo TR 973 air flow indicator may be used to indicate air flow levels of the TR 600 and TR 800 series PAPRs when used with tight fitting face pieces. The TR 973 is designed to enable testing at various elevations and temperatures within the operational range of the PAPR system. The TR 973 is designed to used with the TR 600 blower.