410 A. M. BATEMAN MILITARY AND GEOLOGIC MAPPING 



and negative on the other. Sloj^es may thus be read to one-quarter of a 

 degree. 



The advantages of this slope-card over the slope-board are : Its greater 

 reading accuracy; the fineness of the line of sight, due to its stability on 

 the plane-table ; greater speed of work ; it is unaffected by wind ; and the 

 operation of sighting and determining the angle of slope is independenr, 

 whereas in reading by a swinging pendulum one is forced to determine 

 the reading while the line of sight is being made ; also, the whole instru- 

 ment is detached from the sketching board itself, tlius allowing several 

 slopes to be read without having to change the position of the table. The 

 slope-card may also be used for simply leveling the board when consider- 

 able accuracy is needed for intersections, and with careful manipulation 

 an error of a quarter of a degree need not be exceeded. 



2Q|g 12 8 4 9 



IOC 



Figure 4. — Method of (lividinrj a Line of irregular Length into a given Number of equal 

 Parts to obtain proper Units of Strides 



The angle B A C is assumed ; A C is of any lengtti which is readily divisible into the 

 desired number of units. B C are joined, and the other points projected by lines parallel 

 to BC. 



SCALES 



Pace scales of 1/1000, 1/2000, 1/2500, and 1/5000 were made for 

 each individual stride. Scales based on miles per inch instead of the 

 metric system might also be used if desired. The scale problem was 

 first made on a sheet of paper and the measurements then transferred 

 directly on the wood of an 8-inch triangular ruler. Each scale can be 

 used as a smaller or larger scale by adding or dropping a digit to eacli 

 division. An example of a scale construction follows : 



Construct a scale of 1/1000 for a man whose stride is determined to 

 be 64 inches; scale to read 120 strides, divided into units of 20 strides, 

 with left-hand division divided into units of 2 strides. 



To do this, note that — 



1 inch on scale = 1,000 inches on ground = 15.62 strides; therefore. 



