The phrase "add up again" refers to the act of rechecking or reviewing previously calculated figures or computations to ensure their accuracy. Some common synonyms for this phrase include "recalculate," "recount," "recheck," "double-check," and "verify." Each of these terms essentially describes the same action of going back over numbers or processes to make sure that everything is correct and nothing was missed. Additionally, other related terms like "audit," "scrutinize," and "examine" may also be used depending on the context and purpose of the review. Overall, it is important to thoroughly check and confirm any calculations or data to avoid any mistakes or errors.