the  body  of  the  machine  fits  comfortably  in  the palm of the hand, and the rotating eraser can be directed  as  accurately  as  a  pencil  point.  Refills  for either ink or pencil erasing are available. CAUTION:  Do  not  hold  the  electric  eraser steady in one spot, or you may easily wear a hole or  damage  the  surface  of  the  material  being erased. When there are many lines close together and only  one  needs  to  be  removed  or  changed,  the desired  lines  may  be  protected  by  an  erasing shield,  as  shown  in  figure  2-5. Finely  pulverized  gum  eraser  particles  are available  in  squeeze  bottles  or  in  DRY  CLEAN PADS  for  keeping  a  drawing  clean  while  you work  on  it.  If  a  drawing  or  tracing  is  sprinkled occasionally with gum eraser particles, triangles, T squares, scales, french curves, and the like, not only tend to stay clean themselves, but also tend to   clean   the   drawing   or   tracing   as   they   are moved  over  the  surface. Before  a  drawing  is  inked,  it  is  usually prepared  by  sprinkling  on  POUNCE  (a  very fine  bone  dust)  and  then  rubbing  in  the  pounce with  a  felt  pad  on  the  container.  Pounce  helps to  prevent  a  freshly  inked  line  from  spreading. A  draftsman’s  DUST  BRUSH  should  be  used for  brushing  dust  and  erasure  particles  off  a drawing. 29.273 Figure 2-5.-Use of an erasing shield. DRAFTING  TABLES  WITH  BOARDS Most EA shops are furnished with standard drafting tables with drafting boards, as shown in figure  2-6.  The  majority  of  this  furniture  is easily adjustable to the users’ needs. The height of the table should be such that if you desire to work in a standing position, you can do so without stooping   or   holding   your   arms   in   a   raised position.  Hinged  attachments  for  the  drafting board  are  provided  to  adjust  the  incline  so that  your  line  of  sight  will  be  approximately perpendicular   to   the   drafting   surface.   Your drafting stool should be high enough in relation to  the  table  for  you  to  see  the  whole  drafting board but not so high that you are uncomfortably seated. The drafting boards contained in the drafts- man   kit   are   constructed   of   joined   strips   of softwood, usually clear white pine or basswood. They are equipped with hinged attachments for securing the board to a table or fabricated base. If suitable bases are not available, table bases may be constructed at the unit carpenter shop. You  should  consider  only  the  left-hand vertical edge as a working edge for the T square if you are right-handed (the right-hand edge if you are  left-handed).  The  T  square  should  never  be used  with  the  head  set  against  the  upper  or  lower edge of the board, as the drafting board may not be  perfectly  square. The  drafting  board  should  be  covered.  A variety  of  good  drafting  board  cover  material  is available. Available cover materials are cellulose acetate-coated paper, vinyl, and mylar film. The vinyl  drafting  board  covers  have  the  added advantage  of  being  able  to  close  up  small  holes or cuts, such as those made by drafting compasses or  dividers.  In  general,  these  covers  protect  the drafting board surface by preventing the drafting pencil   from   following   the   wood   grain,   by reducing   lighting   glare,   and   by   providing   an excellent  drafting  surface. Since you will be constantly using your eyes, it  is  important  that  your  working  area  be  well lighted.  Natural  light  is  best,  if  available  and ample,   although   in   the   majority   of   cases acceptable  natural  light  will  be  the  exception rather than the rule. Drafting rooms are usually lighted   with   overhead   fluorescent   fixtures. Ordinarily, these fixtures are inadequate in quality and   intensity   of   light.   Adjustable   lamps   will improve  the  lighting  conditions.  The  most  popular type  of  adjustable  lamp  is  the  floating-arm fluorescent fixture that clamps onto the drafting 2-6