The RCP sits in the architectural set. It shows acoustical tile grids, drywall ceilings, soffits and ceiling heights. It also shows lights, diffusers and sprinkler heads.
An acoustical ceiling sub measures square feet of each ceiling type from it. An electrician counts fixtures by type and checks them against the fixture schedule.
Read the ceiling legend first. Then check heights room by room. Compare the architectural RCP with the electrical lighting plan, because fixture counts can differ.
Ceiling-hung items such as gym equipment or operable partitions may appear here too. Check the structure above them.