To measure Daylight Opening (DLO), measure the visible glass, from stop to stop.
To measure the Tip-to-Tip dimension, measure the longest part of the surround (perimeter) portion of the grille, on the top of the profile (the portion that faces outward from the glass).
To measure the Underneath dimension, measure the shortest part of the surround (perimeter) of the grille, on the bottom of the profile (the portion that touches the glass).
