2i6 Forestry Quarterly. 



dry and free from dirt. A clean sheet stimulates neatness in the 

 field work of the compass-man. 



When in the field, a sudden shower may render a map sheet 

 unfit for further use. The compass-man should be able to pro- 

 ceed on his strip after the rain with a clean, dry sheet and should 

 be able to store his wet map sheet separate from the dry map 

 sheet. Later the field work of both sheets can be collected on 

 one map sheet. 



The materials used must not warp out of shape or split. The 

 metal parts, if metal is used, must not be of iron or steel. No 

 bright finished metal should be used, in order to avoid sun glare. 



The map sheet Jwldcr must be adapted for use as a plane table 

 in addition to being used as a tatum holder in the hand. 



Often when proceeding along the strip the compass-man has 

 opportunities to sight upon lakes, spurs of ridges, and other con- 

 trolling points of topography at one side of his line. He can take 

 a compass sight to the point and plot the compass bearing using 

 the standard compass as a protracter. But this takes time- If 

 the compass-man can quickly mount his map sheet holder on a 

 Jacob staff the sights can be taken and plotted with greater speed 

 and with as great accuracy. Again, a strip may end at the edge 

 of a steep cliff or rim of a crater. The timber cover may not 

 call for an estimate. The compass-man may find it profitable to 

 traverse the rim using the map sheet holder as a plane table. He 

 can locate points of horizontal control below him by intersection 

 and obtain vertical control with an Abney level. At any time the 

 compass-man must be able to convert his map sheet holder into 

 a plane table and vice versa. 



The following difficulties are encountered. The compass-man 

 must be able to dismount the plane table and prepare to carry it 

 between stations with ease and speed and with as few manipu- 

 lations as possible. 



The extra weight of the Jacob staff, which must be carried, is 

 unavoidable. 



With the above mentioned requirements in view an attempt 

 has been made to design a plane table-sketching case to accom- 

 modate the standard reconnaissance map sheets of the Forest 

 Service- The complete field equipment of the compass-man 

 would call for the following : 



