212 Forestry Quarterly. 



the level was common at first, such as recording 7 degrees for 2 

 degrees — or vice versa — or 15 degrees for 5 degrees — or vice 

 versa — the error in the first case being 11.6 feet, and in the second, 

 23.9 feet. Very small angles were often recorded with the wrong 

 sign, as minus 2 for plus 2, the error in this case being 9-2 feet. 



Error due to change in degree of slope frequently happens, 

 especially along the top of ridges where ledges are common, and 

 along the foot of slopes where the creek bed forms the bottom. 

 In these cases, taking only one hundred link sights would often 

 suffice, but very often this led to the error of neglecting to divide 

 the tabular value by two. Or the actual distance from a station 

 to the point of change of slope was measured. Then the hori- 

 zontal distance was computed and from that the elevation of the 

 point of change. This necessitated another computation in get- 

 ting the additional distance for the full chain, a proceeding which 

 is unpopular with the level man especially if he understands 

 merely the method and not the reason therefor. So it usually 

 resulted in the inaccurate method of adding links for a certain 

 degree of slope when a change in degree resulted in an indetermi- 

 nate error. With a level man who understands thoroughly what 

 his work is. this class of error would be eliminated. 



Errors in computation were very uncommon for the reason 

 that the level man checked his work at the end of each acre, by 

 adding all plus and minus readings, separately, and adding or 

 subtracting the difference between them to, or from, the elevation 

 at the beginning of the acre. 



The topographer used a sheet of co-ordinate paper ruled in 

 fifths of inches — each division representing 200 links. The strip 

 lines were run five chains, or one linear acre apart, and it was a 

 ver>' easy thing to sketch the contours for a distance of 500 links 

 on each side of the line. All features of the terrain were sketched 

 in by the topographer, and their location noted in his book, by 

 the level man. 



A circuit was selected at random from among the tally sheets 

 of several months work which showed the following: 



Total distance, 5 . 12 miles. 



Total plus readings, 2,127 ^^^t. 



Total minus readings, 2,284 feet. 



Total difference in elevation, 4,4ii feet. 



