This is what I DON'T like about paper and pen methods of voting: "About half the time these numbers don't, so we recount everything a few times until they do."

This is what I DON'T like about paper and pen methods of voting: "About half the time these numbers don't, so we recount everything a few times until they do." There are errors. How can you guarantee that when the numbers finally do match, that there still isn't any errors on the count? Maybe +1 was added to a candidate, -1 for another, and now the numbers match.