It is normal for projects to go through what is known as a shakedown period after final acceptance and occupancy by the client or building tenant. The warranty and guarantee period (normally 1 year) is the contractors representation and recognition that certain building elements and systems may need adjustment or slight modification, depending on actual occupancy conditions or normal maintenance and usage of such systems. The heating, ventilating, air conditioning, and systems unique to a project require testing and balancing and potential minor modifications and adjustments during this warranty and guarantee period, even though they were tested and balanced by the contractors testing agency prior to project closeout. An independent testing and balancing contractor who was employed prior to final project closeout normally returns on an as-needed, on-call basis to adjust, test, and balance systems during the first year. In addition, the building engineer will become familiar with the systems during this first year of operation and may also adjust and balance systems.