In this activity, learners use simple items to construct a device for indicating air pressure changes. Learners build aneroid barometers (also known as "dry" barometers) and record the level of the straw for 10 days. Learners observe how the changes in straw level relate to the changes they notice in the weather. This lesson guide includes background information about the history of barometers, how barometers measure air pressure, and how pressure relates to weather and thunderstorm safety. Learners can also build a "wet" barometer by following the instructions in the related resource.