22 AGRICULTURAL ENGINEERING 



The Care and Use of Chains and Tapes. The chain is 

 folded by starting at the middle and folding in the two halves 

 at the same time. It is opened by holding the two handles 

 in one hand and throwing out the chain with the other. 

 The steel tape is wound on a reel or thrown into a coil, the lat- 

 ter method requiring some practice and skill to prevent kinks. 

 Chains and tapes are used in measuring 

 horizontal distances; and for this purpose they 

 should be held horizontal, or level, when meas- 

 uring, not parallel to the surface of the ground. 

 The chain or tape should be pulled taut enough 

 to overcome the shortening due to the sag. 

 Where distances are to be obtained with great 

 accuracy, the chain or tape should be tested 

 often over a known fixed distance to determine 

 the amount of pull necessary to bring it to 

 the true length. Chains in constant use re- 

 quire frequent adjustment for wear. 



Each pin should be so placed that its thick- 

 ness will not be added to the length of the chain. 

 Care should be taken to set the pins vertical. 

 When chaining up or down slopes, one end of the 

 chain must be held high to make it level, when it 

 becomes necessary to transfer a point from the 

 elevated end vertically to the ground. This can 

 best be done with a plumb-bob and string, and 



rig. 5. 



a wooden when this is not at hand a pin may be dropped 



range pole. 



from the elevated end of the chain or tape and 

 the point where it strikes the ground noted. 



In chaining practice, the man leading is called the head 

 chainman, and the other the rear chainman. In beginning 

 a measurement, the rear chainman marks the starting point 

 with one of the eleven pins in the set, and gives the remain- 



