The Ponchon–Savarit graphical construction allows the rigorous computation of the number of equilibrium stages in the case of the separation of a binary mixture composed of -hexane and -octane. This graphical method uses both material and energy balances to determine the number of theoretical stages required to achieve a specific separation. The column has a partial condenser and reboiler. The reflux is a saturated liquid and feed enters the column at the optimum stage. The value of is determined by the program and the ratio of reflux to distillate flow rates at the top stage is chosen such that . The tie lines are shown in purple. The operating lines for the stripping and rectifying sections are shown in cyan and green, respectively. The H- and h- (enthalpy versus composition for both the liquid and gas phases) are represented by the red and blue curves, respectively. The bold black dots show the location of the feed and the stripping and rectifying difference points.