How a GPS Glitch Can Change the Taste of Your Salad

Much of the automated world depends on satellites. When one has a problem, it can cause startling butterfly effects.

Satellites can reveal themselves in unexpected, even astonishing ways, and not only by flaring in the sun of an evening horizon, like artificial stars. Their presence can also be inferred indirectly—by causing subtle, nearly undetectable problems elsewhere, such as a briefly wandering tractor.

In Pinpoint, his new book about GPS, the satellite-based Ground-Positioning System, author Greg Milner explores, among other things, the world of precision agriculture, where semi-automated field equipment is guided not by a farmer’s steady hand but by signals sent from machines in space.