46 Forest Club Annual 



Further data was obtained in Ohio in the survey of woodlots 

 which were dense enough to require considerable clearing before 

 sights could be taken. The topography, however, was not so 

 difficult as that in the sand hills, since there were definite drain- 

 age lines giving regular valleys and ridges. In one instance an 

 area of eight acres was covered in one-half day. Another area 

 of thirty acres was covered in two days giving an average of 

 about fifteen acres per day. The size of party and contour in- 

 terval were the same as in the first case. 



The accuracy of the instrument has been tested in the field 

 and the sources of error determined. The most important of 

 these errors is probably the measurement of the horizontal distance 

 in the field. The reading of the plumb line and the variation of 

 the depth to which the staff is forced into the ground are also 

 important but if the instrument is correctly constructed and care- 

 fully used all errors are largely compensating and, in closing ele- 

 vations on a traverse, the error should not be more than ten feet 

 and is usually less. In running a traverse of thirty-five hundred 

 feet there was an error of one foot in closing elevations. In 

 another of three thousand feet the error was three feet. In 

 three others varying from five hundred to one thousand feet 

 the error varied from six inches to one foot. Such 'errors will 

 usually be experienced because of the crudeness of the instrument 

 but will not seriously affect most maps required in forestry. 



