Amount to an expected or correct total, as in These figures don't add up, meaning they are not correct. [Mid-1800s]
Be consistent, make sense, as in I'm not sure that all this testimony will add up. [First half of 1900s]
Assess, form an opinion of, as in He looked across the track and added up the competition. Also see add up to.
Dictionary.com presents 366 FAQs, incorporating some of the frequently asked questions from the past with newer queries.