I have two closely-related questions, which are probably just one question: 1. On the National Weather Service website (http://www.srh.noaa.gov/jetstream/atmos/ll_airweight.htm),it [Broken] says "When we measure air pressure, we are measuring the weight of a column of air 15 miles (24 km) high directly over us." So what are we measuring when we measure the air pressure in the International Space Station? 2. If I took an open screw-top container down a hundred meters below water and put a pressure-gauge inside it, the gauge would, presumably, measure the weight of the liquid above it. Would the reading then change if I screwed a strong top tightly shut onto the container? Presumably the liquid inside the container is no longer supporting the weight of the water above it (the top is doing that); and the liquid inside the container has not been compressed very much, so the pressure it is exerting on the gauge it is surrounding does not come from being compressed by the (previous) weight of the liquid above it (unlike, I assume, the identical case for a pressure gauge inside a sealed container of air, on the surface).