The barograph (Figure below) is a recording barometer. In principle it is the same as a non-recording aneroid barometer except that the pointer carries a pen at its outer end, and A clock mechanism inside the cylinder rotates it so that a continuous line is traced on the chart to indicate the pressure at any time. The barograph is usually mounted on a shelf or desk in a room open to the atmosphere, in a location which minimizes the effect of the ship's vibration. Shock absorbing material such as sponge rubber may be placed under the instrument to minimize vibration. The pen should be checked and the inkwell filled each time the chart is changed.

A marine microbarograph is a precision barograph using greater magnification and an expanded chart. It is designed to maintain its precision through the conditions encountered aboard ship. Two sylphon cells are used, one mounted over the other in tandem. Minor fluctuations due to shocks or vibrations are eliminated by damping. Since oil filled dashpots are used for this purpose, the instrument should never be inverted. The dashpots of the marine microbarograph should be kept filled with dashpot oil to within three-eighths inch of the top. The marine microbarograph is fitted with a valve so it can be vented to the outside for more accurate pressure readings.

Ship motions are compensated by damping and spring loading which make it possible for the microbarograph to be tilted up to 22° without varying more than 0.3 hPa from the true reading. Microbarographs have been almost entirely replaced by standard barographs.

Both instruments require checking from time to time to insure correct indication of pressure. The position of the pen is adjusted by a small knob provided for this purpose. The adjustment should be made in stages, eliminating half the apparent error, tapping the case to insure linkage adjustment to the new setting, and then repeating the process.

• Zone Time In Celestial Navigation - 2009-04-21 - 01:09:16
• Some common local winds are listed by local name - 2009-04-21 - 12:35:43
• Wind Patterns - Modifications of the General Circulation - 2009-04-21 - 05:46:03
• Maneuvering to Avoid the Storm Center - 2009-04-21 - 05:03:03
• Weather Routing - Benefits - 2009-04-19 - 07:35:50
• Weather Routing - Communications - 2009-04-19 - 07:25:17
• Weather Routing - Southern Hemisphere Routing - 2009-04-19 - 07:21:29
• Weather Routing - Types of Recommendations and Advisories - 2009-04-19 - 07:16:12
• Special Weather and Environmental Considerations - 2009-04-19 - 07:06:59
• Weather Routing - Synoptic Weather Considerations - 2009-04-19 - 06:15:22

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