The barograph is an ideal instrument to use for weather forecasting because it automatically writes a continuous record of atmospheric pressure change over a seven day period. Changes in pressure may occur during the night and would be missed by an ordinary barometer especially if changes occur rapidly. This detailed record makes forecasting weather more accurate.
Barometers and barographs have pressure capsules that shrink and expand as atmospheric pressure changes. The barograph has a mechanical linkage system that connects the changes in the pressure capsule to a pen on the end of a long arm. The pen records these changes on a piece of graph paper attached to a rotating drum. Some drums are electrically powered. Most of the antique barometers you see here are powered by clock movements usually on a 7 day cycle.