How to make your own Barometer! Remember, a Barometer is the weather instrument used to measure Air Pressure or Atmospheric Pressure. The unit of measurement is millibars. You can do some weather forecasting yourself simply by making your own Barometer. What you need. An empty coffee jar A large balloon A large elastic band, one that will fits tightly around the coffee jar. A pin Glue / Tape A Straw Paper Card Instructions. 1. Cut a large piece of the balloon and stretch it over the jar. 2. Use the elastic band to hold the balloon in place. Make sure there is a tight seal around the rubber band. Any air leaks around the piece of balloon will affect how well your barometer will work. 3. Glue or tape the straw to the balloon on top of the jar. 4. Glue or tape the pin to the end of the balloon. (See diagram.) 5. Take a piece of paper card (20cm high x 8cm wide) and mark a series of evenly spaced lines on it. Use another piece of card to make a stand so your paper card can stay upright. 6. Set up the can and paper as shown in the diagram. Your barometer will work better outside than inside. Using Your Barometer Check your barometer a few times each day for one week. Record what is happening to the pin on the barometer, and then record what the weather is like at the time you take the recording. How Does It Work? When the air pressure rises, it puts more pressure on the balloon, pushing the balloon down into the jar. This pushes the pin up higher on the scale. When the air pressure gets lower, it puts less pressure on the balloon. The balloon rises up and the pin goes lower on the scale. In general, low air pressure means that we will have rainy or cloudy weather. In general, high air pressure means that we will have dry sunny weather.