What does harmonic mean mean?
harmonic mean. Noun
1. (mathematics) ; A type of measure of central tendency calculated as the reciprocal of the mean of the reciprocals, ie, 
  
    
      
        H
        =
        
          
            n
            
              
                
                  1
                  
                    x
                    
                      1
                    
                  
                
              
              +
              
                
                  1
                  
                    x
                    
                      2
                    
                  
                
              
              +
              ⋯
              
                
                  1
                  
                    x
                    
                      n
                    
                  
                
              
            
          
        
      
    
    {\displaystyle H={n \over {1 \over x_{1}}+{1 \over x_{2}}+\cdots {1 \over x_{n}}}}
For example, If an and bn denote the perimeters of inscribed and circumscribed regular n-gons, respectively, along some circle then the harmonic mean and geometric mean of those two perimeters yield the perimeters of the inscribed and circumscribed regular 2n-gons, respectively, along that same circle. (This is Archimedes' Recurrence Formula.)
