operations in which mistakes are possible. Some of  the  more  common  mistakes  are  as  follows: .  Failing  to  hold  graduations  plumb  over p o i n ts . Involuntarily transposing figures, such as recording  48.26  for  48.62 l Misreading figures that are viewed upside down, such as recording an upside-down 9 as a 6 .  Reading  a  subdivided  end-foot  from  the wrong end, as, for example, 0.28 ft instead of 0.22 ft .  Associating  subdivided  end-foot  reading with wrong whole-foot mark, as 38.21 ft instead of  37.21  ft .  Subtracting  incorrectly  when  using  a  minus tape .  Omitting  an  entire  tape  length RECOGNIZING   COMMON   ERRORS.— There  are  two  types  of  errors:  accidental  and systematic. An  accidental  error  is,  generally  speaking,  one that may have a varying value. Examples are as follows:   variation   of   the   tension   applied   to the  tape,  inaccurate  sticking  of  pins  or  other markings, and inaccurate determination of slope. Accidental  errors  can  be  minimized  by  careful- ness,  but  not  entirely  eliminated. A   systematic   error   has   a   constant   value. The  standard  error  in  a  tape,  for  example, is  a  systematic  error.  Temperature  and  sag corrections  are  applied  to  correct  systematic errors. Systematic errors can be compensated for or  otherwise  eliminated  by  the  application  of corrections. Caring for and Maintaining a Survey Tape If a steel or metallic tape gets a kink in it, it is then subjected to strain. The tape at best will be distorted at the point where the kink lies. At worst, if the strain is strong enough, the tape will break  at  the  point  where  the  kink  lies.  Kinks, therefore,  are  to  be  avoided  at  all  costs;  it  is especially important to avoid putting a strain on a tape with a kink in it. Under favorable circumstances, when a tape is shifted ahead, the head chainman may simply drag it over the ground. It is not a good idea for the rear chainman to assist by dragging that end because  this  develops  a  curve  in  the  tape.  This curve may snag on an obstruction and also may be  the  cause  of  a  kink.  When  a  tape  is  being dragged, the rear chainman should simply allow the end to trail along. The cardinal rule is “keep, the  tape  straight.” When taping in traffic, you plan your moves in advance and make the measurement as fast as possible.   If   possible,   do   not   let   vehicles   run over   the   tape;   however,   if   this   is   absolutely unavoidable, be sure the tape is laid flat and taut on the road. NEVER let a vehicle run over a tape laid  on  a  soft  or  rugged  ground  surface. Tapes   are   made   as   corrosion-resistant   as possible, but no steel tape is entirely immune to corrosion,   especially   when   used   around   salty water. Therefore, a tape should always be wiped dry before it is put away, and it should be oiled periodically with a light, rust-resistant oil. If a tape does rust, rubbing it with light steel wool dipped in a rust-removing compound is the best and safest way  to  remove  the  rust.  Tapes,  especially  those in reels, though not used during the week, should be  removed  from  the  reel  and  inspected  each  week for  signs  of  corrosion.  A  damp  climate  in  your area of operations could easily start corrosion in tapes. Splicing a Tape In  spite  of  being  carefully  handled,  tapes sometimes  break.  A  broken  tape  is  rejoined  by splicing.  A  relatively  light  tape  can  be  repaired with  a  punch-and-rivet  tape  splicer  and  repair stock  (fig.  12-22).  A  repair  stock  consists  of  a Figure 12-22.-A punch-and-rivet tape splicer with repair stock. 12-23