maintenance personnel by making it possible for them to visualize the system or object you are explaining. BLUEPRINTS AND DRAWINGS Blueprints are exact copies of mechanical or other types of drawings and employ a language of their own. It is a form of sign language or shorthand that uses lines, graphic symbols, dimensions, and notations to accurately describe the form size, kind of material, finish, and construction of an object. It can be said that blueprint reading is largely a matter of translating these lines and symbols into terms of procedure, materials, and other details needed to repair, maintain, or fabricate the object described on the print. Usually you can look at a blueprint and recognize the object if you are familiar with the actual part. But when you are required to make or check on a certain part, the applicable blueprint must be referred to in order to get dimensions and other pertinent information. The important thing is to know what the different symbols stand for and where to look for the important information on a blueprint. Some of the important facts listed on all blueprints are discussed in the following paragraphs. Title Block The title block is located in the lower right comer of all blueprints and drawings prepared according to military standards. The block contains the drawing number, the name of the part or assembly that the blueprint represents, and all information required to identify the part or assembly. The title block also includes the name and address of the Government agency or organization preparing the drawing, the scale, drafting record, authentication, and the date (fig. 1-71). A space within the title block with a diagonal or slant line drawn across it indicates that the information usually placed in it is not required or is given elsewhere on the drawing. Revision Block The revision block (not shown) is usually located in the upper right corner of the blueprint and is used for the recording of changes (revisions) to the print. All revisions are noted in this block and are dated and identified by a letter and a brief description of the revision. A revised drawing is shown by the addition of a letter to the original number in the title block, as shown in figure 1-71, view A. If the print shown in figure 1-71, view A, was again revised, the letter in the revision block of the title block would be replaced by the letter B. Drawing Number All blueprints are identified by a drawing number (NAVSHIP Systems Command No. in view A of fig. 1-71, and FEC Drawing No. in view B), which appears in a block in the lower right corner of the title block. It may be shown in other places also; for example, near the top border line in an upper corner, or on the reverse side at both ends so that it will be visible when a drawing is rolled up. If a blueprint has more than one sheet, this information is included in the block indicating the sheet number and the number of sheets in the series. For example, note that in the title blocks shown in figure 1-71 the blueprint is sheet 1 of 1. Reference Numbers Reference numbers that appear in the title block refer to numbers of other blueprints. When more than one detail is shown on a drawing, a dash and a number are frequently used. For example, if two parts are shown in one detail drawing, both prints would have the same drawing number, plus a dash and an individual number, such as 8117041-1 and 8117041-2. In addition to appearing in the title block, the dash and number may appear on the face of the drawings, near the parts they identify. Some commercial prints show the drawing and dash number, and pint with a leader line to the part; others use a circle, 3/8 inch in diameter, around the dash number, and carry a leader line to the part. A dash and number are used to identify modified or improved parts, and also to identify right-hand and left-hand parts. Many aircraft parts on the left-hand side of an aircraft are exactly like the corresponding parts on the right-hand side but in reverse. The left-hand parts are usually shown in the drawing. Above the title block on some prints you may see a notation such as “159674 LH shown; 159674-1 RH opposite.” Both parts carry the same number. But the part called for is distinguished by a dash and number. (LH means left-hand, and RH means right-hand.) 1-43