What happens next?

How to build a barometer
Gather your materials.
To make a tin can barometer, you will need a tin can, a balloon, a rubber band, glue, two plastic straws or coffee stirrers, construction paper, and an index card. Most of these items should be easily found around the home.
If you don't have a tin can, any container with a large-mouth (diameter of 1.5-2 inches), plastic or glass, will work for this barometer. A bottle with a narrow mouth will not work.