A barograph is a type of aneroid barometer, and as you see here, the pointer is replaced by a pen.
It also has a drum and bellows.
Every seven days the drum makes one revolution.
A chart, which is affixed to the drum, is graduated in time on one axis and atmospheric pressure in millibars on the other.
The barograph provides a continuous record of the atmospheric pressure.
Since the barograph can be affected by environmental factors, its location should be carefully selected.
Place it in a position that is, as far as possible, free from vibration, loud noise, jostling and gusts of air.
The barograph should be fastened in an athwartships position, so the pen does not leave the paper when the ship is rolling.