The idea
The stillest moment of your life — asleep, motionless, mid-Sunday-nap — you were doing roughly a million kilometres a day. Earth spins, Earth orbits, and the whole Solar System is on a long lap around the Milky Way. You have been aboard for every kilometre.
This instrument adds up the trip. It is the cheapest form of space travel ever devised: you were issued a ticket at birth, and the odometer has been running ever since.
How it’s measured
Three motions do almost all the work. Earth’s orbit carries you at 29.785 km every second. The Solar System drifts around the galactic centre at roughly 230 km/s. And the planet’s spin adds a share that depends on your latitude — about 1,674 km/h at the equator, less as you move toward the poles, which is why we ask where you’ve mostly lived.
We multiply each speed by the seconds you have been alive and add them. Physicists will note — correctly — that these motions point in different directions and that “total distance” depends on your chosen reference frame. Summing the magnitudes gives an honest, easy-to-picture scale of the ride rather than a single frame-perfect trajectory. We say so on the poster, too.
Questions, answered
Distance relative to what, exactly?
The spin figure is measured against Earth’s axis, the orbit against the Sun, and the galactic figure against the centre of the Milky Way. There is no universal “standing still” in physics — every distance needs a reference point, so we show each one separately before totalling.
Why does my location change the number?
Only the spin component depends on it. A point on the equator sweeps out a much bigger daily circle than a point near the poles, so the tropics ride about twice as fast as the far north.
How precise are the speeds?
The orbital speed is known to high precision; the Sun’s galactic speed is measured at roughly 220–240 km/s, so we use 230. Your total is solid to within a few percent — more than enough to feel appropriately dizzy.