To determine where the stair started on the first floor the primary piece of evidence needed was the location of the lowest newel post.  While newel posts primarily support the railing, because the lowest newel post is always closely aligned with a stair's lowest riser, it can be used to determine where a stair begins.  So if the location of a stair's lowest newel is known, where the stair starts on the first floor can be quickly determined.  Fortunately, since the ca. 1797 flooring survived, the Restoration Team was able to find a square patch in the flooring that provided evidence for the location of the stair's lowest newel.