Air-Pressure Difference Monitor
This air-pressure differential monitor provides an accurate, reliable and affordable means to visually monitor a very low positive, or negative, air pressure difference between a room and:
1. Another room or floor level.
2. Soil gasses under the lowest floor.
Undesirable air-pressure differences in buildings can cause air movement and leakage in ways that adversely affect health, comfort, energy costs, and the longevity of buildings.
— Air Pressure and Building Envelopes by Dr. Joseph Lstiburek.