About 2 1 pound per square inch = 2.0362... inches of mercury
5.57742782 feet
30cm are in a feet
A water barometer would have to be many feet tall because the density of water is much lower than that of mercury. In addition, the vacuum above the column would be spoiled by the water vapor pressure, far higher than that of mercury, and strongly temperature dependent.
14öösquare feet
It has a radius of approx 8005250 feet, 244000000 centimetres or 2668416 yards.
12" make a feet.
As close to 30 as makes no difference.
Pressure in these things is measured by how tall a column of liquid it can support. Now atmospheric pressure can support many feet of oil, for example, and who wants a barmeter that tall? Mercury is very dense so you can get away with less than a metre high. Problem solved.
1 inch of mercury is equal to 1.133 feet of head.
1.524 meters are in five feet.
19 feet = 228 inches.