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How does GPS work?

TomTom Education


The early days of navigation

To avoid getting lost, our ancestors had to do everything from erecting huge landmarks to burning hilltop bonfires. The basic principles of navigation have changed very little.

Before a way was discovered to accurately determine longitude, there was no way of knowing how far east or west you were. So right up until the late 1700s, once out of sight of land, sailors simply had to estimate their longitude on the basis of how far they thought they’d travelled. They did this by something called dead-reckoning. Using the formula Velocity x Time = Distance, the sailor could work out the distance he’d travelled by multiplying the time he’d been sailing by the speed of his ship.

As you can see in the GPS section, exactly the same mathematical formula lies at the heart of GPS. The only difference being degrees of error. But that’s quite a difference, because whereas GPS uses atomic clocks to measure time, these sailors only had an hourglass; and while GPS employs trilateration and radio signals to calculate distance, the old sailors made do with watching pieces of seaweed pass by the hull!

When you stop to think for a moment what it would take to draft a detailed map without access to any modern science or technology, you realize how ingenious the early navigators had to be.


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