in pressure what does mmHG mean?

Answer 1

millimeters of mercury

At standard atmospheric pressure, a vacuum will support 29.92 inches of mercury (760 mmHG). At standard atmospheric pressure, a vacuum will support about 33 feet of water.

Answer 2

Take a tube with mercury in it (no air above the surface of the mercury) inverted over a dish of mercury. Air pressure pushes down on the dish of mercury causing the mercury to go up the tube. Measure, in millimeters, how high the mercury goes above the dish of mercury. You have now measured the pressure in "mm of Hg". If the air pressure goes up, the mercury rises higher; if the air pressure goes down, the mercury goes down.
(you could use other liquids, like water. But then the tube would have to be much bigger and you would need a ladder to measure how high the water rose)

Because the unit "mm of Hg" can easily be understood this way, we have to give it a new name so "science" can remain a mystery to the uneducated (and because scientists hate to write; that's why we abbreviate everything). So, the unit "mm of Hg" has been changed to "Torr" in honor of the Italian scientist Torricelli. Now, what used to be 760 mm of Hg is written as 760 Torr.

Answer 3

millimeters of mercury

"The torr (symbol: Torr) or millimeter of mercury (mmHg) is a non-SI unit of pressure. It is the atmospheric pressure that supports a column of mercury 1 millimeter high. The unit is named after Evangelista Torricelli, Italian physicist and mathematician, for his discovery of the principle of the barometer in 1643. A related unit is the micrometre of mercury (µmHg), which is one thousand times smaller."

Answer 4

Millimeters of Mercury

Answer 5

millimeters of mercury