Okayyyy, so after a little searching apparently zeroing with RO can miscalibrate your reading. Not sure by how much considering I've never had a problem.  
 
That being said I will do the loop, find some of this solution and get back to you guys as to how far off the reading is from zero. 
		
	
		
		
		
		
			
		
		
		
		
	
		
		
	
	
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