e equation 
 
                | T(et-lt) - O(et) | 
         lt = ------------------------                            (1) 
                         c 
 
      The ratio  
 
          | T(et) - O(et) | 
        ---------------------                                     (2) 
                  c 
 
      is used as a first approximation to 'lt'; inserting (2) into the
      right hand side of the light-time equation (1) yields the
      &quot;one-iteration&quot; estimate of the one-way light time (&quot;LT&quot