I am always amazed at the amount of time and anguish some people will devote to completing reports - especially those useless ones required by the state or a central office.
Here's how I look at them:
If there is money involved, I attempt to be as accurate as possible without agonizing. When ever possible, I figure conscientious estimates are enough. I mean, is somebody actually going to come in and recalculate the average age of your science section? Re-measure the square footage of your media center? Really care if you count a set of reference books as one title or three volumes? Sit and monitor the average number of students who visit the media center? I don't think so.
As my dad always said, "A job not worth doing is not worth doing well." Give a good guess and then use your time helping your kids or staff. The world will continue to revolve.