PLANE TABLE. 



27 



except as noted below. If the lines do not intersect, the 

 orientation may be changed until they do, but an easier 

 plan is to fasten a piece of tracing cloth on the table 

 and assume a point from which the lines may be drawn 

 toward the peaks. The tracing may then be shifted 

 over the paper to find a position at which the lines will 



FIG. 8. Plane-table method of finding location from three points. 



exactly cover the three needle holes on the paper. This 

 method is reliable when the desired location is within 

 the triangle, but it is useless when the table is set up on 

 or near a circle which would pass through the three 

 peaks. For this reason four or more points should be 

 used if possible. (See fig. 8.) 



