It is the number of things done, not doing something, one thing, all day.
You remember, i did 10 things today, and so, that took a long time. Instead of like, fighting with the plumbing all day, and at the end of the day, you pretty much did not one thing.

And we can never answer the tree falling question, because whenever we look however we look, it will always make a sound.

However, even bugs and worms have consciousness and so, the tree makes noise for them too.