WHAT IS BAROMETRIC PRESSURE?

Barometric pressure is the air gas molecules pressure on the Earth's surface. The actual barometric pressure varies with temperature, weather and elevation.

In meteorology and aviation, the barometric pressure is always given as calculated mean sea-level pressure (QNH) to compensate for pressure changes as function of elevation. In higher altitude the lower air density provides a lower barometric pressure.

Barometric pressure is measured by measuring the absolute pressure using a diaphragm sensor with an integrated reference vacuum. Barometric pressure can also be measured by a mercury column gauge; however, mercury gauges are discontinued or forbidden in most countries due to worker safety hazards and environmental issues when incorrectly disposed of.