started, the rear chainman watches the tai1 end (100-ft mark) of the tape as the head chainman moves  forward. 3. When the rear chainman sees that the tail end  is  about  to  reach  his  position,  he  calls “Chain!” At that time, the head chainman stops and  looks  back.  The  rear  chainman  holds  the 100-ft mark at the starting point and checks the alignment;  then  signals  the  way  the  head chainman should move the chaining pin to be in line. While doing this, they are both in a kneeling position,  the  rear  chainman  facing  the  distant point, and the head chainman to one side facing the line so that the rear chainman has a clear view of  the  range  pole.  The  head  chainman,  while stretching  the  tape  with  one  hand,  sets  the  pin vertically  on  line  a  short  distance  past  the  zero mark  with  the  other  hand.  Then  by  pulling  the tape taut and making sure that the tape is straight, the head chainman brings it in contact with the pin,  The  rear  chainman,  watching  carefully  for the 100-ft mark to be exactly on the point, calls “All right!‘’ The head chainman relocates the pin to  exactly  the  zero  mark  of  the  tape  and  places it  sloping  away  from  the  line.  He  then  pulls  on the tape again to make sure that the zero mark really matches the point where the pin is stuck in the   ground.   Then,   he   calls   “All   right!”   or “Stuck!”  This  is  a  signal  to  the  rear  chainman to release the tape so he can continue forward for the  next  measurement.  The  process  is  repeated until the entire distance is measured. 4.  As  the  rear  chainman  moves  forward,  he pulls the pin from his point. Thus, there is always one pin stuck in the ground; therefore, the number of pins in his possession at any time indicates the number of 100-ft (stations) tape lengths they have measured from the starting point to the pin in the ground. Every  time  the  head  chainman  runs  out  of pins,  he  signals  the  rear  chainman  to  come forward, and both of them count the pins in the rear chainman’s possession. There should be 10 pins. SUPPORTING  THE  TAPE.—  When a full tape length is being measured, the two chainmen support the ends of the tape. The tape maybe laid on a level ground surface, such as a paved road or railroad rail, or suspended between stools or bucks set under the ends of the tape. For precise measurement, such as base line measurement, the tape is supported at midpoint or even at quarter points  by  bucks  or  stakes. In horizontal taping over sloping or irregular terrain, one end of the tape is held on the point at ground level, while the other end is supported high  enough  to  make  the  tape  horizontal.  As shown  in  figure  12-12,  the  rear  chainman  is holding a full graduation of the tape at the point near  the  ground,  and  the  head  chainman,  holding the zero end, projects the desired distance to the point  on  the  ground  by  using  the  plumb  bob. ALIGNING  THE  TAPE.—   Any   misalign- ment  of  the  tape,  either  horizontally  or  vertically, will   result   in   an   error   in   the   measurement. Misalignment always results in a recorded distance that is too great, or a laid offline that is too short. This  is  obvious,  since  the  shortest  distance between two points is a straight line. Keep the tape straight and level at all times. APPLYING TENSION.— A tape supported or held only at the ends will hang in the shape of a curve, called a catenary, because of its own weight. Depending on the tension or pull applied at the ends,   this   catenary   will   become   shallower   or deeper; and the distance between the supported ends will vary considerably. To standardize this distance, you should apply a recommended “stan- dard” tension when you are measuring. You should attach a spring balance or tension handle to one end of the tape and measure the correct standard tension.  The  amount  of  standard  tension  is  dis- cussed  later  under  “Making  Tape  Corrections.” Maintaining  a  constant  tension  for  any  length of time by a hand pull is uncomfortable and can be erratic. For easier chaining, each chainman uses a pole or rod about 1/2 to 2 in. in diameter and about 6 ft long. The leather thong attached to the tension handle is wrapped around the pole at the proper height. The chainman braces the bottom end of the pole against the outside of his foot and applies tension by bracing his shoulder against the Figure 12-12.-Horizontal taping on a slope. 12-12