I just read David McCollough's "The Wright Brothers," and was surprised to find several references to the exact altitude attained by various Wright airplanes. For example, on page 235:
The next day came news from Potsdam, Germany, that Orville had flown to an altitude of 984 feet, higher than anyone had yet flown in an airplane.
The flight in question occurred in 1909. But the altimeter would not be invented until 1928. How can anyone be certain that such a specific altitude was reached? I don't see any instrumentation in the photos of their aircraft. Was the altitude calculated from the ground somehow?