Pressure

Atmospheric pressure is a fact that influences even the human body. The globe is surrounded by a layer of air about 965 km high, this height is measured from sea level. The layer of air that forms the atmosphere puts pressure on the surface of the earth. And what would be the value of this pressure? The normal atmospheric pressure is approximately 1 Kgf in each cm², at sea level. Therefore, atmospheric pressure can be thus defined:
Atmospheric pressure is the force that the layer of air surrounding the earth exerts on its surface.
Pressure measurements at atmospheric pressure are obtained by applying the following formula:
P = Kgf / cm²
At where:
P = pressure
Kgf = force
Cm² = area
As you can see, two units of measurement are involved in the calculation of the atmospheric pressure: Kgf (kilogram-force) and m² (square meter). How did this measure come? Evangelista Torricelli reached a value of 1.03 Kgf / cm² through the barometer, an instrument he invented. Torricelli's barometer consisted of a glass tube, one meter long, with a cross section of 1 cm², closed at one end.
To measure atmospheric pressure at sea level, he filled the glass tube with mercury (Hg), capped the open end with his finger, and inverted the position of the tube, plunging the capped end with the finger into an open container and also with mercury . Taking his finger off the end, he observed that some of the mercury in the tube went down to a height of 76cm above the mercury in the open container. He concluded that atmospheric pressure at sea level exerted pressure on the mercury in the vessel, balancing the mercury column of the tube. At this value it assigned 1 atm, that is, 1 atmosphere, which is approximately 1.03 kgf / cm². Because? Because 1cm³ of mercury is equal to 13.6g. Therefore, to know the weight (mass) of the mercury column of 76cm, simply multiply 76cm by 13.6 and ÷ 10. The result is equal to 1.03kg.
Therefore :
1 atm = 1 atmosphere
1 atm = 1.03kgf / cm²
1 atm = 76cm of mercury or 760mmHg