How to use ALPHA MOTO motorcycle vacuum carburetor synchronization gauge

This vacuum gauge by far has the highest quality on the market, it is made in Taiwan. This set features 4 precision gauges. Each gauge is pre-calibrated by factory, air flow control is handled by needle and seat valves instead of knob it comes with both 5mm and 6mm adapters, will work with virtually all bike models with carburetors.
Comes with case, four gauges, adapters and hoses.
This vacuum gauge by far has the highest quality on the market, it is made in Taiwan. This set features 4 precision gauges. Each gauge is pre-calibrated by factory, air flow control is handled by needle and seat valves instead of knob it comes with both 5mm and 6mm adapters, will work with virtually all bike models with carburetors.
Comes with case, four gauges, adapters and hoses.

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One of my gauges is stuck at 0 - I switched the hose with one of the working gauges, to confirm. I adjusted the flutter tight and lose. Is this faulty, or am I missing something?