Weems and Plath Endurance 125 Clock - Manual (Page 14)

Barometer Operating Instructions
A barometer is an instrument used to predict a change in weather by
measuring variations in atmospheric pressure, or the weight of the air
around us. The barometer will normally indicate changes in weather 12 to
24 hours in advance. It is not an indicator of present weather conditions.
Your barometer is an aneroid type which measures atmospheric
pressures mechanically without use of liquids.
Your barometer can be mounted indoors as the pressure will be the same
as outdoors. Don’t take any notice of the words Rain, Change, Fair. They
are there only as a traditional graphic decoration. At sea level the normal
atmospheric pressure is about 30 inches, very rarely will the needle ever
exceed 30.5 or drop below 29.5. Sometimes it is possible for the pressure
to only change one or two tenths of one inch over a week or so. Even a
storm may only make a half inch change.
When your barometer left the factory, it was set at standard sea level. It is
necessary for you to calibrate it to the atmospheric pressure in your area
by turning the small screw found on the back of the movement. Never turn
this screw in either direction more than one full rotation.
Contact your local weather bureau for current atmospheric pressure and
adjust your barometer accordingly. For every 100 feet in altitude an
adjustment of 0.11 inch is required (1000 ft. = 1.1 inch). The movement
used in this barometer is adjustable up to an altitude of 3500 feet.