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Some facts I learned or renewed today, while I was looking at this chart.

Picture from Slovenian Environment Agency - Aviation

Nautical mile is approximately one minute of arc of longitude only at the equator. How to calculate altitude from an atmospheric pressure? The answer is here. Click. Or if you need a formula, it is here:
z = (RT/gM).log_e(p_o/p), where z is the height difference between the starting height and the measurement height, R is the gas constant, T is temperature of the air measured in Kelvin, g is the acceleration due to gravity, Mis the molar mass of the gas (in this case air), po is the atmospheric pressure at the starting height and p is the atmospheric pressure at the measurement height.