On the Type 1 Fix, the two small notches at the top and bottom edge of the Fix are to help marking out: The notches may be used to mark, or line up the centreline of the Fix. By also marking out, and drawing a line through the centre of the screw holes, the centre point of the Fix may be determined, which is also the point at which the Button will sit once installed. Alternatively, to avoid the need for precise measuring of the button and fix positions, the Type 1 and Type 2 Button marker accessory tools may be used. For detailed instructions of how to mark out/set out Button-fix please see the relevant Instructions for use document under the useful information tab.