Works in Progress: Measuring Mount Everest

Four pounds doesn't feel like a lot when it's a bag of groceries you're schlepping out to the parking lot. But if you're lugging it up to the top of Mount Everest, four extra pounds in your pack can feel like a ton. The climbers who took a four-pound GPS receiver to the summit of the world's highest mountain last year were convinced nonetheless that the extra weight would be worth the effort. That's because GPS--short for "global positioning system," a satellite-based network that uses radio signals to determine location--can gauge a mountain's height with an accuracy unequaled by standard surveying methods. Mapmakers hope the new technology will bring some finality to a field long plagued by fuzzy numbers. But like most alpine pursuits, the urge to quantify Everest is largely metaphysical: They measure it because it's there.