Abney Level and the Chain 343 



latter must face the compassman squarely, open the mouth well, 

 and project the sound directly from the mouth rather than from 

 the throat. A throaty sound cannot be picked up easily. The 

 estimator will, as a rule, fail to appreciate the importance of 

 this point until he himself has tried mapping in brushy country. 



The mapper who is trying the hand level for the first time in 

 mapping will wonder how he can possibly run 2 miles of line per 

 day. If the 23/2-chain tape, described earlier in this article, is 

 used, there are 80 sights involved in merely carrying the control 

 aside from perhaps numerous side shots. Every movement made 

 by the mapper must count. No advocate of the use of the Abney 

 hand level and chain will maintain that the line can be run as 

 quickly as with the aneroid barometer and pacing. In my ex- 

 perience, the method will take 10 per cent more time. This con- 

 clusion is based on a comparison of 24 days' work, using the 

 aneroid barometer, with the same number of days' work with the 

 Abney hand level in the same type of country in the Coeur d' 

 Alene Mountains, on a two-man crew. But when the amount 

 of time necessar}' to correct the map made with the aneroid 

 barometer is taken into account, it is seen that there is very little 

 difference. It takes from thirty minutes to one hour to correct 

 a map made with the aneroid barometer, where the curve must be 

 plotted, the day's readings then corrected, and the map adjusted. 

 This offsets almost exactly the 10 per cent additional time needed 

 in the field when the Abney hand level is used. 



The question will arise as to closeness of "checking out." In 

 country in which a 100-foot or a 50-foot contour interval shows 

 the country well, the average error in distance can be made less 

 than one-half chain, the average vertical error less than 25 feet. 

 Time and again the error will be less than 10 feet. 



The results generally obtained with the use of the Abney hand 

 level and the tape are usually satisfactory. A high percentage of 

 the maps made as herein described are among the very best maps 

 made on intensive forest surveys in the United States. Timber 

 appraisers, lumbermen, and logging engineers, who are, as a rule, 

 exacting in map requirements, have found them to stand the test. 



