How a pressure gauge works

Picked one by one from a mixed channel. Transcript check: both title readers certain; channel sample of 8 certain picks all confirmed by transcript. Channel rule: Include long-form videos whose titles plainly name the subject and the mechanism explained (e.g. 'How a pressure gauge works', 'How the Colosseum Actually Worked', 'Inside the USS Monitor: How It Actually Worked', 'How Wooden Sailing Warships Were Built'), and exclude titles built on withheld-information or hype hooks.