 In a modified form with clearly defined geometrical proportions, this quadrilateral may now serve as a reference model for the definition of the articulation of further vowels. The proportions of this reference model or coordinated systems are clear and this is how to construct it. First we need a top line which is four measures in length and it is drawn horizontally. Then we need a second line which is the right hand vertical line which is three measures in relationship to the four measures of the top line and the angle between the two lines is 90 degrees. The bottom line is half as long as the top line and again we have an angle of 90 degrees between the vertical right hand line and the bottom line. And finally we now link the three ends of the two horizontal lines so that we get the basic dimensions of the cardinal vowel chart.