y]2 Forestry Quarterly. 



indicated in the table is given in the nearest 2 per cent. Ordinar- 

 ily, it adds nothing to the practical accuracy of the work to read 

 the Abney closer. When long sights are taken the exact per cent 

 can be read and the elevation determined a little closer by interpo- 

 lation. The paces, too, are indicated in the table to the nearest 5. 

 It seems to add nothing to the practical accuracy of the work 

 to indicate this more closely. 



The use of the table is very simple. 



The compassman first sets up his compass, secures an alignment^ 

 and then sights with the Abney level at some object along the 

 compass course at approximately the height of his eye. The 

 slope (plus or minus) is then noted on the field map, as indicated 

 in the accompanying sketch. The compassman then paces to the 

 object sighted at, which is usually a point where the slope cnanges. 

 He then refers to the table already prepared and pasted on the 

 front cover of his tatum holder and directly determines the rise 

 or fall in elevation. He adds or subtracts this to the elevation 

 previously established at the starting point. This takes but a mo- 

 ment's calculation and usually it is a mental one. The true ele- 

 vation as determined is noted on the map to the left of the strip 

 line. The station indicated in paces is set down on the map at 

 the right of the strip line. He then draws a form line contour 

 through the station and proceeds with his observation for the 

 next station. 



It is always best to sight at some object approximately the 

 height of the eye, but this is not at all necessary, especially when 

 long sights are taken. For distances over 75 double paces the dif- 

 ference in per cent by sighting at an object several feet above 

 or below the height of the eye is so small that it can not be read 

 on the Abney scale. It is not advisable to take observations for 

 distances much over 200 paces unless the object sighted at is very 

 distinct. Because the table does not give direct differences in 

 elevation for horizontal distances greater than 100 double paces 

 it should not be assumed that this difference in elevation can not 

 be obtained. For distances over 100 double paces note the read- 

 ing for 100 double paces and then add to it the reading for the 

 additional distance. The sum of the readings gives the dif- 

 ference in elevation between the two points. 



In cruising the most economical crew is 2 men. The compass- 



