104 
X mm 
— 
_ 
  
  
T —T— 
60 80 ()() m 
  
  
  
T T T 
- 80 - 60 —40 - 20 
T 
— 100 
10 
15 
  
  
  
  
  
earth’s curvature. 
(in microns) of the #’-coordinates due to the 
Errors 
Diagram 31.