The ozone layer lies mostly 15 to 35 km up and blocks most of the Sun's most harmful ultraviolet rays. Yet if all that ozone were brought down to ground-level pressure and temperature, it would form a film about 3 mm thick, roughly two stacked coins. That is what the Dobson unit measures: 300 units equal 3 mm.
On 27 August 1883, the eruption of the Indonesian volcano Krakatoa was heard as far away as Rodrigues Island, nearly 4,800 km away. Its pressure wave was picked up by barometers worldwide and circled the globe several times. The tsunamis that followed killed more than 36,000 people.
The deepest known point in the ocean, Challenger Deep, lies roughly 10,900 m below the Pacific surface. Drop Everest in and its summit would still sit about 2 km underwater. Down there, the pressure is more than 1,000 times what you feel at sea level, roughly a tonne pressing on every square centimetre.