This value 
  
    
      
        
          c
        
      
    
    {\textstyle \mathrm {c} }
   is used in the above equations for determining 
  
    
      
        
          
            K
          
          
            
              c
            
          
        
      
    
    {\textstyle \mathrm {K} _{\mathrm {c} }}
  .Following this test, the sample can then be reoriented such that further loading of a load (F) will extend this crack and thus a load versus sample deflection curve can be obtained.
This is done by taking the test piece with its fabricated notch of length 
  
    
      
        
          c
          ′
        
      
    
    {\textstyle \mathrm {c\prime } }
   and sharpening this notch to better emulate a crack tip found in real-world materials. Cyclical prestressing the sample can then induce a fatigue crack which extends the crack from the fabricated notch length of 
  
    
      
        
          c
          ′
        
      
    
    {\textstyle \mathrm {c\prime } }
    to 
  
    
      
        
          c
        
      
    
    {\textstyle \mathrm {c} }
  .