baker's dozen

[L]et him caſt his Eye upon the laſt Page of that Book, where Mr. Blount has tranſlated a Quotation out of Scaliger de Emend. brought by the Author of the Præadamitæ; now he tranſlates Octingenties octagies, not eight hundred and eighty, but eight hundred and eightſcore; as if the Romans had uſed to reckon by ſcores. He might altogether as well, have made them number by Bakers-Dozens.

"Before I agree to help you and your baker's dozen over there …" Rose nodded at Larry. / "It means cousin," Larry said. / "Before I say yes to helping, I would like a low-risk, up-front agreement."