Abney Level and the Chain 341 



form is that shown below, in which the first cokimn gives the 

 chains or feet, the second the per cent, and the third the actual 

 elevation. 



2+34—3295 



4+20—3321 



6—22—3292 



The putting down of the per cent will enable one to locate 

 more easily later any mistakes in figuring the elevation. The 

 notes should be put on the margin or on the back of the map 

 sheet. 



The following table gives the difiference of two points, on slopes 

 of different per cents, the points being 2 chains apart horizontally. 



Table of Difference of Elevations for 2-Chain Distance 



No table is needed where a 100-foot tape is used, the per cent 

 slope giving the difference of elevation at once. When the 300- 

 foot tape is used, the per cent slope must be multiplied by 3 to give 

 the difference of elevation. 



All forest surveys offer difficulties which must be overcome, 

 and chances for errors which must be guarded against. The new 



