The distance used to calculate the pressure of atmosphere is 75 cm.
Explanation:
Mercury barometer is used to find the pressure of the atmosphere where it is placed.
As shown in the figure, the barometer has an inverted tube where mercury has risen by 75 cm. This height is taken into count to measure the atmospheric pressure.
At the place with high pressure the mercury in the inverted tube will go very high and vice versa.
Hence to find the pressure we must note down the height of mercury that has risen the inverted tube.
