For the benefit of those who, for the first time, may meet new terms and expressions in this manual, the following vocabulary, with definitions, is appended:<br><br>Altitude. Vertical height.<br><br>Angle. Space between two intersecting lines.<br><br>Apex. Point where converging lines meet.<br><br>Apices. More than one apex.<br><br>Arc. Any part of the circumference of a circle.<br><br>Area. Surface in units of measurement.<br><br>Bisect. To cut in two equal parts.<br><br>Bisector. A line which bisects.<br><br>Chord. The line connecting any two points of an arc of a circle.<br><br>Circumference. The boundary of a circle.<br><br>Circumscribe. To draw around.<br><br>Convention. Customary method or symbol used in producing a drawing.<br><br>Decagon. Figure of ten sides and ten angles.<br><br>Degree. One 360th part of a circle.<br><br>Diameter. The distance measured across the center of a circle or a line drawn through the center terminating in the circumference.<br><br>Element. A part which goes to make up the whole.<br><br>Elevation. A view of an object looking at the front or side.<br><br>Elliptical. Pertaining to the shape of an ellipse.<br><br>Equilateral. Equal-sided.<br><br>Frustum. Remaining portion of a cone or pyramid when the top has been removed parallel to the base.<br><br>Hemisphere. Half a sphere.<br><br>Heptagon. Figure of seven sides and seven angles.<br><br>Hexagon. Figure of six sides and six angles.<br><br>Horizontal. Parallel to the horizon.<br><br>Hypotenuse (spelled also Hypothenuse). The diagonal distance between opposite angles of a rectangle or the side opposite the right angle.<br><br>Isometric. Of equal measurement.<br><br>Isosceles Triangle. A triangle with two sides of equal length and base angles equal.<br><br>Lateral. Side.