'Meter, Ground Flow Check (Oxygen System). By Sperti, Inc. of Ohio. The Ground Flow Check Meter was designed to check the operation of the A-8 & A-9 series oxygen regulators. This operation was done while the regulator is permanently installed in the aircraft and the aircraft is on the ground. The instrument consists of a length of hose for connection to the regulator, a handgrip and the main body containing the rotameter unit and thermometer. This example is in unused condition complete with bakelite storage case and outer card box dated May 1943. Instructions for use are printed on a sheet within the lid of the storage case. The instructions are stained otherwise excellent throughout.