Attractive aneroid barometers, give it a tap when you come downstairs in the morning and see what the weather is likely to do today.
An aneroid barometer is a weather forecasting instrument used to measure the changes in barometric pressure. Once adjusted to the elevation above sea level, it shows rises and falls in the air pressure, sometimes just a tap on the front of the glass is all it takes for the needle to jump to the right position. The dial is marked in millibars and often shows from Stormy to Very Dry and gives an indication of what the weather may be like, although it perfectly feasible to have high pressure (showing very dry) and then having a torrential thunderstorm.

Original barometers were operated using a tube of mercury, which rose and fell with the pressure but due to the high cost and the dangers of mercury, a new system was developed using a metal pressure box called an aneroid. An aneroid box effectively expands & contracts at a set rate depending on how high above sea level.