not even a finger's breadth

We indeed (to repeat in conclusion what we have mentioned several times above) have wished, in this work of concord, in no way to devise what is new, or to depart from the truth of the heavenly doctrine which our ancestors, renowned for their piety, as well as we ourselves, have acknowledged and professed. We mean that doctrine, which, having been derived from the Prophetic and Apostolic Scriptures, is contained in the three ancient Creeds, in the Augsburg Confession, presented in the year 1530 to the Emperor Charles V, of excellent memory, then in the Apology, which was added to this, in the Smalcald Articles, and lastly in both the Catechisms of that excellent man, Dr. Luther. Therefore we also have determined not to depart even a finger’s breadth either from the subjects themselves, or from the phrases which are found in them, but, the Spirit of the Lord aiding us, to persevere constantly, with the greatest harmony, in this godly agreement, and we intend to examine all controversies according to this true norm and declaration of the pure doctrine. -- Intro to the book of Concord, 1580