Ship's Bell 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 your Chelsea Clock barometer leaves our factory, it is adjusted to register pressure at the local pressure of Chelsea, MA. However, because atmospheric pressure decreases as altitude increases, if you live in a higher-altitude location you’ll need to adjust your barometer (corrected to sea level) to receive an accurate reading. To do this, call your local weather bureau and ask for the present barometer reading. Adjust your barometer’s navy blue indicator hand to the reading given by turning the screw on the back of the case. The hole that will be used to access the set screw will be indicated by an “S” stamped next to the hole. If you live at an altitude of 2,500 feet or greater, your barometer should be adjusted professionally. 

Tip: Before taking a reading, lightly tap on the barometer glass to release any built-up frictional resistance on the indicator dial.

Care & Service

Caring for your Barometer Case

Chelsea Clock cases are made of high-quality brass, superbly polished and lacquered for long-lasting beauty and protection. However, dust, fingerprints and environmental pollutants may, over time, mar the finish. To help maintain its bright finish, we suggest cleaning the case weekly with a clean, soft cloth. Never use polishes, cleaners or other liquids, as these can tarnish and pit the finish.

Servicing your Barometer

Based on normal operating conditions, our technicians recommend that your Chelsea clock be cleaned, oiled and adjusted about every seven years. Conditions such as extreme heat, cold, dust and prolonged idleness can necessitate more frequent servicing.

Your Chelsea Clock barometer is a precision instrument and should only be serviced by a certified repair technician. We suggest returning your item to our factory repair center for guaranteed service by an experienced Chelsea technician.