MEASUREMENT OF DISTANCE 11 



broken tape can generally be repaired on the ground if there 

 are at hand a punch, a piece of another tape, and some pins 

 to serve as rivets. 



3. ]\IARKING PINS 



Woodsmen frequently manufacture their own marking 

 pins of wood or wire. Those bought from dealers are 

 made of heavy iron wire, are some fifteen inches in length, 

 with one end sharpened and a ring turned in the other for 

 convenience in handling. Strips of cloth are tied in the 

 rings, so that they can be readily seen. It is most con- 

 venient to use eleven pins in chaining. One of them is 

 stuck at the starting point, the leading man takes ten, 

 and thus there is always one in the ground to start from 

 when the tallies are finished. 



4. CHAINING PRACTICE 



Chains are standardized in length at about ten pounds 

 pull with their full length supported. In woods work it is 

 generally necessary that the chain should be suspended 

 above the ground and not lie upon its surface. Care must 

 be taken, therefore, in accurate measurement, to give it 

 proper tension. What tension is proper for a suspended 

 chain, in other words, what sag should be allowed to 

 compensate for the stretch of the chain under the greater 

 tension may be determined on perfectly smooth and level 

 ground, and this is a valuable exercise for inexperienced 

 chainmen. 



In order to get true chainage between points, the chain 

 should be kept straight and free from kinks. It must also 

 be kept in approximately true alignment, though a con- 

 stant error of 1 in that matter, equivalent to seven inches 

 error in setting pins each two rods of distance, shortens 

 the line by only nine and a half inches in the mile. Simi- 

 larly, the chain must be levelled so as to give distance in 

 a horizontal line, not following the contour of the ground. 

 In this last connection, that is, in getting distance correctly 

 on slopes and over rough ground, are met the greatest 

 difficulties in practical chaining. What is necessary is 

 first, to determine when the chain is level, and second, to 



