Mercury barometers used today work on the same principle as Torricelli's device. A mercury barometer consists of a glass tube of mercury with a reservoir at the bottom. Any change in air pressure will cause the mercury in the tube to rise and fall. There is a scale beside the tube that indicates the pressure. Besides measuring pressure, barometers are used to measure altitude.
Pilots use barometers to determine their altitude.
Hikers and mountain climbers may also use barometers to measure altitude.