text: obtained is approximately 75 percent of the 
  speed for maximum range. 
  
  A more exact analysis of range may be ob- 
  tained by a plot of specific range versus velocity 
  similar to the second graph of figure 2.23. Of 
  course, the source of these values of specific 
  range is derived by the proportion of velocity 
  and fuel flow from the previous curve of fuel 
  flow versus velocity. The maximum specific 
  range of the airplane is at the very peak of the 
  curve. Maximum endurance point is located 
  by a straight line from the origin tangent to 
  the curve of specific range versus velocity. 
  This tangency point defines a maximum of 
  (nmi/lb.) per (nmi/hr.) or simply a maximum 
  of (hrs./lb.). 
  
  The final graph of figure 2.23 shows a typical 
  variation of specific range with gross weight 
  for some particular cruise operation. At the 
  beginning of cruise the gross weight is high 
  and the specific range is low. As fuel is con- 
  sumed, and the gross weight 
  reduces, the 
  type of curve 
  specific range increases. .This’ 
  relates the range obtained by the expenditure 
  of fuel .by the crosshatched area between the 
  gross weights at beginning and end of cruise. 
  For example, if the airplane begins cruise at 
  18,500 Jbs. and ends cruise at 13,000 lbs., 5,500 
  lbs. of fuel is expended. If the average spe- 
  cific range were 0.2 nmi/Jb., the total range 
  would be: 