One dot on a map, earned from falling signals. Follow it from first glance to the moment it lands on you.
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This is a curated, step-through lesson, not a receiver. The chart is a flat stand-in for a sphere: real GPS solves crossings in three dimensions, with at least four satellites so the receiver clock is solved as an unknown too. Ranges here are illustrative, not measured. Challenge answers are practice, not a measure of mastery.
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The lesson shows the civilian core idea. Real receivers track more than four satellites across several constellations, correct for atmosphere and relativity, and refine the dot constantly. What stays true is the order of ideas: time, rings, clock, shape.