CHAIN SURVEYING 27 



Steel tapes are now used extensively in surveying and are 

 largely superseding both the engineers' and the surveyors' 

 chain. They can be obtained in any length from 1 yd. to 

 1,000 ft. and graduated to order. For city surveying, and for 

 many other purposes, a tape 50 ft. long is generally preferred. 

 For some purposes, tapes 300 or 500 ft. long and even of greater 

 length are used. In some tapes, the handle forms part of the 

 end division or graduation, the length of the tape counting 

 from the outside of the handle. In others, the graduations 

 begin on the inside of the handle, where the tape is attached, 

 and in others the graduations begin on the tape itself, a short 

 distance from the handle. When using a tape, the surveyor 

 should ascertain where the graduations begin, as otherwise he 

 may make serious errors. The tape has sometimes attached 

 to it a handle that contains a spring balance for measuring the 

 pull on the tape, a level bubble to guide in holding the tape 

 so that it will be level, and a thermometer to show the tem- 

 perature of the tape. 



Correction for Erroneous Length of Chain. The length of 

 a chain or tape is altered by changes in temperature, and by 

 wear and distortion. The variations due to temperature are 

 very small, and need to be considered only in very accurate 

 work. The alterations due to wear and distortion are some- 

 times considerable. 



The length of the chain should be tested often. This is 

 done either by comparing the chain with a chain or tape of 

 standard length, or by stretching it between two points whose 

 exact distance apart is known. It is advisable to have two 

 such points marked permanently on an office floor, smooth 

 pavement, curb, or some other convenient place. 



If, after a line has been measured, the length of the chain 

 (or tape) is found to be in error, the true length of the line 

 can be easily determined by means of the following formula: 



in which Lo = true length of line; 



L = length of line as actually measured; 



e = error in length of one unit of measure. 

 If, for instance, the length of a line is measured in feet, and 

 the measurements are made with a 50-ft. tape that is found to be 



