“Usable Piece” means that portion of the potato remaining after trimming, or as it occurs in the sample:
    
    
        
        (a) 
         Not have any unusable material;
     
    
        
        (b) 
         Unless otherwise specified, weigh at least 4 ounces; and,
     
    
        
        (c) 
         Must have at least 50% of peel remaining after trimming.