Uni-Syn Model A Carburetor Synchronizing Tool.
Here we have the classic "one hand" synchronizer.
Light, compact and versatile, it can be used on virtually all carburetors that require synchronising of the throttle valves.
The foam-padded back ascertains a good seal against the carburettor and the red indicator will show you the measured airflow.
The indicator swivels over some 120 degrees which allows you to use it in the tightest of spaces and still get a good reading.
Suitable for carburetors / trumpets of between 35 and 75 mm in diameter (1.8 - 3.8 inches).
A true classic !