by a letter and a brief description of the revision. Arevised drawing is shown by the addition of a letter tothe original number, as in figure 1-1, view A. When theprint is revised, the letter A in the revision block isreplaced by the letter B and so forth.Drawing NumberEach blueprint has a drawing number (fig. 1-1,views A and B), which appears in a block in the lowerright corner of the title block. The drawing number canbe shown in other places, for example, near the topborder line in the upper corner, or on the reverse sideat the other end so it will be visible when the drawingis rolled. On blueprints with more than one sheet, theinformation in the number block shows the sheetnumber and the number of sheets in the series. Forexample, note that the title blocks shown in figure 1-1,show sheet 1 of 1.Reference NumberReference numbers that appear in the title blockrefer to numbers of other blueprints. A dash and anumber show that more than one detail is shown on adrawing. When two parts are shown in one detaildrawing, the print will have the drawing number plusa dash and an individual number. An example is thenumber 811709-1 in the lower right corner of figure1-2.In addition to appearing in the title block, the dashand number may appear on the face of the drawingsnear the parts they identify. Some commercial printsuse a leader line to show the drawing and dash numberof the part. Others use a circle 3/8 inch in diameteraround the dash number, and carry a leader line to thepart.A dash and number identify changed or improvedparts and right-hand and left-hand parts. Many aircraftparts on the left-hand side of an aircraft are mirrorimages of the corresponding parts on the right-handside. The left-hand part is usually shown in thedrawing.On some prints you may see a notation above thetitle block such as “159674 LH shown; 159674-1 RHopposite.” Both parts carry the same number. LHmeans left hand, and RH means right hand. Somecompanies use odd numbers for right-hand parts andeven numbers for left-hand parts.1-4Zone NumberZone numbers serve the same purpose as thenumbers and letters printed on borders of maps to helpyou locate a particular point or part. To find a point orpart, you should mentally draw horizontal and verticallines from these letters and numerals. These lines willintersect at the point or part you are looking for.You will use practically the same system to helpyou locate parts, sections, and views on largeblueprinted objects (for example, assembly drawingsof aircraft). Parts numbered in the title block are foundby looking up the numbers in squares along the lowerborder. Read zone numbers from right to left.Scale BlockThe scale block in the title block of the blueprintshows the size of the drawing compared withthe actual size of the part. The scale may be shown as1= 2, 1= 12, 1/2= 1´, and so forth. It also maybe shown as full size, one-half size, one-fourth size,and so forth. See the examples in figure 1-1, views Aand B.If the scale is shown as 1= 2, each line on theprint is shown one-half its actual length. If a scale isshown as 3= 1, each line on the print is three timesits actual length.The scale is chosen to fit the object being drawnand space available on a sheet of drawing paper.Never measure a drawing; use dimensions. Theprint may have been reduced in size from the originaldrawing. Or, you might not take the scale of thedrawing into consideration. Paper stretches andshrinks as the humidity changes. Read the dimensionson the drawing; they always remain the same.Graphical scales on maps and plot plans show thenumber of feet or miles represented by an inch.A fraction such as 1/500 means that one unit on themap is equal to 500 like units on the ground. A largescale map has a scale of 1= 10´; a map with a scaleof 1= 1000´ is a small scale map. The followingchapters of this manual have more information on thedifferent types of scales used in technical drawings.Station NumberA station on an aircraft may be described as a rib(fig. 1-3). Aircraft drawings use various systems ofstation markings. For example, the centerline of the
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