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