Why do parts of both barometers need to be airtight?

Parts of both barometers need to be airtight to ensure accurate pressure measurements. An airtight seal prevents air from entering or escaping, which could otherwise alter the internal pressure and lead to incorrect readings. Additionally, it helps maintain the integrity of the liquid inside, such as Mercury or another fluid, ensuring it responds accurately to changes in atmospheric pressure. This airtight design is crucial for the barometer to function properly and provide reliable data.