The undersurface (22) of the floorboards (10) is used as a main reference for taking measurements in a tongue and groove floorboard quality control process. The process comprises measuring at least one distance (X, Y) between the undersurface (22) and a downwardly facing surface of at least one of a tongue and a groove profile of selected ones of the floorboards (10). Measurements can be taken from the undersurface (22) of the selected boards (10) on both sides thereof to vertically adjust the relative position of groove cutter head (18) and the tongue cutter head (16) of the molding machine (M) used to manufacture the boards (10). A depth gage (G) can be used to take the measurements.