Zone Pressure Diagnostics is under used, underrated, and misunderstood. Discover how and when to use zone pressure diagnostics (ZPD); and when not to use it. ZPD can help answer many questions, such as: Was the air sealing in the attic effective? Is the attached-garage air entering the house? Is the basement air leaking into the attic? The most advanced ZPD calculation tool will be used, free and available to everyone.