Instructions for the Use and Care of Chelsea Shipstrike and Nautical Barometers

Your barometer is an instrument for measuring atmospheric pressure, or the weight of the air surrounding us. Variations in atmospheric pressure are usually an indication of a coming change in the weather. The barometric pressure generally indicates changes 12 to 24 hours in advance. therefore, we watch the barometer to anticipate and forecast, not as an indication of current conditions.

Your barometer is an aneroid or holosteric type. That is, it measures pressure mechanically, without the use of fluids, by means of an evacuated hollow metallic diaphragm. Change in atmospheric pressure on this diaphragm actuates the pointer or indicator hand on the dial. It is not necessary to mount your barometer outdoors since it will operate properly inside.

The barometer scale is graduated in inches, millibars and centimeters as a measurement of atmospheric pressure. At sea level, normal atmospheric pressure is approximately 29.92 inches, 1014 millibars and 76 centimeters. The average variation in pressure normally encountered at any given altitude is approximately 1" to 1 1/2" either way from the average. Frequently, for many days at a time, the variation and attendant movement of the black indicator is confined to a very lmited area.

The gold plated hand on the glass is a marker hand to be set over the indicator hand when a reading is taken. This marks the presurre at the time of the reading so that subsequent change may be readily noted. A gentle tapping on the glass with index finger will cause the indicator hand to move for a more precise reading.

Adjusting Barometer to Local Altitude (cannot be adjusted above 3500 feet)

When it left the factory, your Chelsea barometer was adjusted to correct pressure at sea level, which is standard for measurement of barometric presure regardless of location or altitude. Since atmospheric pressure decreases as altitude increases, if you are located in a higher altitude your barometer will indicate the lower pressure. It will be necessary then for youi to adjust it to give you a reading corrected to sea level.This is done as follows:

  1. Call your local weather bureau for the present barometer reading.
  2. If the correction is less that 0.30 inches this is done by turning the set screw located just inside the hole in the back of the case with a small screwdriver.
  3. If the correction is 0.30 inches or more, the black indicator hand must be removed and placed at the correct reading. This is done by carefully lifting it straight up from the hub, being careful not to bend the hand or arbor, The hand is replaced with gentle, firm pressure of the tumb. A final adjustment is then made as in 2 above.


Your clock case is constructed with a very high-quality brass, then plated and lacquered for appearance and protection. Chenicals contained in ordinary fingerprints or dust are harmful to the finish.

DO NOT apply polish, cleaner or other liquid to the clock case as this will result in pitting and tarnishing.

To remove harmful chemicals from the surface, we recommend you wipe your case with a soft cloth weekly. Treated with care, the lacquer seal will not be broken and your clock will retain its bright appearance.