The width of all letters and numbers is measured across the greatest distance from the outermost points of the letters or numbers. The width of the letters and numbers is calculated according to a percentage of the height by the number of blocks the figure represents. In other words, to obtain the percentage of the height, divide the width of the figure by the height. Examples: 1. The letter N is 6 blocks high, as are all the figures, and 4.5 blocks wide; therefore, the width of the letter should be 75 percent of the height (4.5/6 = 75%). 2. The letter A is 5.5 blocks wide, therefore, the width should be 92 percent of the height (5.5/6 = 92%). 3. The letter W is 6.5 wide; therefore, the width should be 108 percent of the height (6.5/6 = 108%). The sides of some letters and numerals should be made to include an angle of 30 degrees with the tops or bottoms, as shown in figure 14-31. The space between the letters and numerals is constant. It is always one-sixth of the height of the letter or numeral. This distance is always measured from the point on each of the letters or numerals that is nearest the other. National Insignia The national insignia consists of a white, five-pointed star inside a blue circumscribed circle. A white rectangle, one radius of the blue circle in length and one-half the radius of the blue circle in width, is located on each side of the star. The top edges of the rectangle form a straight line with the top edges of the horizontal two-star points beneath the top start point. A red horizontal stripe one-sixth of the radius of the star is centered in the white rectangles at each end of the insignia. A blue border, one-eighth the radius of the blue circle in width, outlines the entire design. When the insignia is applied on a sea blue, dark blue, or black background, the blue circle and border may be omitted. The inside edge of each interior rectangle is concave and has the same arc as the inside blue circle. The inside edge of each outer rectangle should not be depicted. See figure 14-32. You may refer to MIL-STD-216 1(AS) for more information on the national insignia. Tactical Paint Schemes Tactical paint schemes are used for deception, for reduction of detection range, or to confuse and mislead observers. Tactical paint scheme patterns are applied to an aircraft to lessen the probability of visual or photographic detection. This applies to an aircraft that is in flight or on the ground. The patterns are based on optical principles and use nonreflective colors, color configurations, and color proportions. Arbitrary applications of markings and color schemes will reduce the effect of tactical paint schemes and should not be used. All tactical paint schemes should comply with Paint Schemes and Exterior Markings for U.S. Navy and Marine Corps Aircraft, MIL- STD-2161(AS), and Finishes, Organic, Weapons Systems, MIL-F-18264D(AS). Tactical paint schemes are usually comprised of either two or three shades of gray or blue. The standard material for the tactical paint scheme coating system and common insignia and marking application is lusterless MIL-C-83286 aliphatic polyurethane.    Decals may be used instead of paint for insignia and markings provided they are made of a nonreflective material and meet the gloss requirements of the coating system. Decals should not be used to apply large markings, such as the national insignia. The use of MIL-C-83286 is not required to apply aircraft unit markings. PAINTING EQUIPMENT AND MAINTENANCE PROCEDURES The equipment and techniques used to paint aircraft are covered in this section. You will frequently use and maintain spray guns, air compressors, and regulators. Therefore, the material in this section should be important to you. Spray Guns The spray gun atomizes the material to be sprayed. You direct and control the spray pattern by manipulating and adjusting the spray gun. Spray guns are usually classed as either suction feed or pressure feed. The types are divided by two methods-the type of container used to hold the paint material and the method in which the paint is drawn through the air cap assembly. 14-36