The most common type of barometer—the aneroid barometer—contains no fluid. Inside this instrument is a small, flexible metal box called an aneroid cell. Before the cell is tightly sealed, air is partially removed, so that small changes in external air pressure cause the cell to expand or contract. The size of the cell is calibrated to represent different pressures, and any change in its size is amplified by levers and transmitted to an indicating arm, which points to the current atmospheric pressure.
PRINCIPLES OF BAROMETER
Inside this instrument is a small, flexible metal box called an aneroid cell. Before the cell is tightly sealed, air is partially removed, so that small changes in external air pressure cause the cell to expand or contract. The size of the cell is calibrated to represent different pressures, and any change in its size is amplified by levers and transmitted to an indicating arm, which points to the current atmospheric pressure.
INSIDE VIEW OF THE BAROMETER
LOCATION ON THE BRIDGE
How to Read a Barometer
Barometer has 2 pointer, the black and the gold. The black indicator hand always points to the current air pressure while the gold indicator hand can be used as guide from your last reading to easily observed changes of pressure and can be adjusted manually. Change to high pressure means good weather is ahead while a change to low pressure means bad weather is on the way.
Rising barometer
A gradual but steady rise indicates settled fair weather. A very slow rise from a low point usually means high winds and dry weather. A rapid rise indicates clear weather and very windy. A rise is the black indicator moving in a clockwise direction.
Falling barometer
A gradual but steady fall indicates unsettled or wet weather. A very slow fall from a high point usually means wet unpleasant weather without much wind. A sudden fall indicates sudden rain or snow or high winds or both. A fall is the black indicator moving in an anti-clockwise direction.