![]()  | 
	
| 
		 
			 
			#3  
			
			
			
			
			
		 
		
	 | 
|||
		
		
  | 
|||
| 
		
	
		
		
		
		 
			
			Square root of 81 is 9. 
		
		
		
		
		
		
		
		
	
	4 (power of scope) multiplied by9 = the diametre in mm. of front glass (ie,36 mm.).  | 
		
  | 
	
		
  |