Naval Deck Barometer Manual

How it Works 

A barometer measures changes in atmospheric pressure, or the “weight” of the air. Changes in pressure typically foretell changes in the weather. Weather watchers will note a barometer’s reading and how much and how fast it rises or falls. Rising pressure signals improving weather; falling pressure indicates deteriorating conditions. Generally, a barometer works best when mounted indoors (away from the elements) where air pressure is the same as that outside.

Your Chelsea Clock barometer is an aneroid barometer, meaning it measures atmospheric pressure without mercury or other fluids. Instead, it uses a vacuum and a hollow metallic diaphragm. Pressure changes on the diaphragm cause the dial’s black indicator hand to move. You can manually position the gold hand over the black hand, and return later to see whether pressure is rising or falling. 

Barometers can measure pressure in inches, millibars or centimeters. At sea level, normal atmospheric pressure is approximately 29.92 inches, 1014 millibars or 76 centimeters. At higher elevations the average pressure will be less as there is less air pressure overhead. Normal weather variations cause pressure to rise or fall an inch or less, so you may see little movement of the black hand for several days at a time. A passing storm often brings rapidly falling pressure.

Setting for Local Altitude

When the Chelsea Clock barometer leaves our workshop, it is adjusted to register pressure at the local pressure of Chelsea, MA. If you live in a higher altitude location, you will need to adjust your barometer to receive an accurate reading. To do this, contact your local weather bureau and ask for the present barometer reading. 

•       Open the bezel assembly on the front by turning the black lock knob counterclockwise. Once the door is open, on the back you will see a flat head screw above plus/minus symbols.

•       Use the flat head screw to set the pressure. Close and screw the lock knob.

If you live at an altitude of 2,500 feet or greater, your barometer should be adjusted professionally.

Care

Your new Chelsea Clock item is designed and crafted for maximum precision and durability.  To help ensure many years of enjoyment, follow these care & use tips:

•       Moisture – This piece is designed to be water-resistant. However, it is not waterproof and should not be submerged in water or subjected to heavy rainfall.

•       Rubber Seal – The inside rim of the hinged bezel has a rubber seal.  Be sure to tighten the bezel’s locking bolt completely when closing to ensure a water-resistant seal.

•       Outdoor Placement – If mounting this piece outdoors, it’s best to place it under a covered area, away from direct sunlight, rain and snow.  Avoid areas affected my extreme shifts in temperature.

•       Lenses – Clear lenses are made from glass.  Clean with a soft, damp cloth. Other materials may cause scratching.