Great explainer. The part about atomic clock synchronization always gets me — the satellites carry atomic clocks accurate to 1 nanosecond, and the system has to account for both special AND general relativistic effects (the satellites experience different gravity AND they're moving fast enough that time dilation matters).

The correction factor is about 38 microseconds per day — small enough to ignore in everyday life but catastrophic for GPS accuracy if unaccounted for. No other engineering system relies on relativistic corrections in its day-to-day operation quite like this.