How did the windshield-mounted sight glass gauge function as a primitive visual indicator?

Answer

It acted like an intravenous drip system, showing fuel slowly dripping into a small bottle

This device was designed to provide a visual cue by having fuel slowly drip into a glass bottle mounted near the driver’s eye level, signaling reserve fuel availability.

How did the windshield-mounted sight glass gauge function as a primitive visual indicator?
inventionVehiclemeasurementtechnologyfuel gauge