is  the  product  of  01´  times  the  square  root  of 3,  or  about  1.73´.  The  prescribed  maximum angular  error  of  closure  has  therefore  been exceeded. Meeting  Precision  Specifications The  following  specifications  are  intended  to give  you  only  a  general  idea  of  the  typical precision requirements for various types of transit- tape surveys. When linear and angular errors of closure  are  specified,  it  is  understood  that  a closed  traverse  is  involved. For many types of preliminary surveys and for land surveys, typical precision specifications may read  as  follows: l  Transit  angles  to  nearest  minute,  measured once. Sights on range poles plumbed by eye. Tape leveled by eye, and standard tension estimated. No temperature or sag corrections. Slopes under 3  percent  disregarded.  Slopes  over  3  percent measured by breaking chain or by chaining slope distance  and  applying  calculated  correction. Maximum angular error of closure in minutes is 1.5 ~n.  Maximum  ratio  linear  error  of  closure, 1/1000.  Pins  or  stakes  set  to  nearest  0.1  ft. For most land surveys and highway location surveys, typical precision specifications may read as  follows: l  Transit  angles  to  nearest  minute,  measured once.  Sights  on  range  poles,  plumbed  carefully. Tape  leveled  by  hand  level,  with  standard  tension by  tensionometer  or  sag  correction  applied. Temperature  correction  applied  if  air  temperature more  than  15°  different  from  standard  (68°F). Slopes under 2 percent disregarded. Slopes over 2  percent  measured  by  breaking  chain  or  by applying  approximate  slope  correction  to  slope distance.  Pins  or  stakes  set  to  nearest  0.05  ft. Maximum  angular  error  of  closure  in  minutes is l~n.  Maximum  ratio  linear  error  of  closure, 1/3,000. For  important  boundary  surveys  and  extensive topographical  surveys,  typical  precision  specifica- tions  may  read  as  follows: . Transit angles by 1-rein transit, repeated four  times.  Sights  taken  on  plumb  lines  or  on range poles carefully plumbed. Temperature and slope  corrections  applied;  tape  leveled  by  level. Pins  set  to  nearest  0.05  ft.  Maximum  angular error of closure in minutes is  0.5~n.  Maximum ratio  linear  error  of  closure  is  1/5,000. Note  that  in  the  first  two  specifications, one-time   angular   measurement   is   considered sufficiently  precise.  Many  surveyors,  however,  use two-line   angular   measurement   customarily   to maintain  a  constant  check  on  mistakes. Measuring Angles vs. Measuring Distances It is usually the case on a transit-tape survey that  the  equipment  for  measuring  angles  is considerably  more  precise  than  the  equipment  for measuring linear distances. This fact leads many surveyors  into  a  tendency  to  measure  angles  with great  precision,  while  overlooking  important errors in linear distance measurements. Making  the  precision  of  angular  measurement greater than that of linear measurement is useless because  your  angles  are  only  as  good  as  your linear  distances.  Suppose  that  you  are  running traverse  line  BC  at  a  right  deflection  angle  of 63°45´  from  AB,  180.00  ft  to  station  C.  You  set up at B, orient the telescope to AB extended, and turn exactly 63°45´00´´ to the right. But instead of  measuring  off  180.00  ft,  you  measure  off 179.96  ft.  Regardless  of  how  precisely  you  turn all  of  the  other  angles  in  the  traverse,  every station will be dislocated because of the error in the  linear  measurement  of  BC. Remember  that  angles  and  linear  distances must be measured with the same precision. IDENTIFYING  ERRORS  AND MISTAKES  IN  TRANSIT  WORK In transit work, errors are grouped into three general  categories;  namely,  INSTRUMENTAL, NATURAL,  and  PERSONAL  errors.  First,  we will discuss these errors, and then, later, we will explain  the  common  mistakes  in  transit  work. Identifying  Instrumental  Errors A transit will not measure angles accurately unless the instrument is in the following condition: 1.  The  vertical  cross  hair  must  be  perpen- dicular to the horizontal axis. If the vertical cross hair  is  not  perpendicular,  the  measurement  of horizontal  angles  will  be  inaccurate. 2.  The  axis  of  each  of  the  plate  levels  must be perpendicular to the vertical axis. If they are not, the instrument cannot be accurately leveled. 13-24