Which instrument measures atmospheric pressure?

**The reasoning** Atmospheric pressure is the weight of air pushing down on Earth's surface. A **barometer** is specifically designed to measure this pressure. It contains mercury or uses aneroid (sealed) technology that responds to changes in air pressure — when pressure increases, the mercury rises or the aneroid chamber compresses; when it drops, the opposite happens. Meteorologists use barometers to predict weather because falling pressure often signals storms approaching. **Why the wrong options tempt you** - **Thermometer** measures temperature (heat), not pressure — easy to confuse because both relate to weather - **Hydrometer** measures liquid density or specific gravity (like testing battery acid or salt concentration in water) - **Ammeter** measures electric current in amperes — completely different field (electricity, not atmospheric science) All these "-meters" sound scientific, so if you're rushing, you might pick any one! **Quick takeaway** **"Baro-" means pressure (like "baric" in isobaric), so barometer = pressure meter.** Link it this way: when you hear about "low pressure systems" on weather forecasts, that's what barometers detect!