Reduction of sextant sight to position fix and plot takes 3-6 minutes in the air (20 minutes , ships @ sea) , but the time needed depends on the before flight home work having been done. Precomputation is of paramount importance in air navigation and is done with the aid of special air navigation tables and an air almanac. On long range flights the navigator checks the DR in a 20 minutes sequence plan by taking sights on heavenly bodies. Generally there is little or no leisure time during flight. These features valid for "navigation old fashion" , although , also with advanced navigation methods , operating and checking the nav instruments is an all time consuming business.