by the yellow line. For sinking air, the starting point on the  vertical scale has been moved up a distance corresponding  to the vertical velocity of the air. Consequently, the red  tangential line contacts the curve at a glide speed higher than  best glide speed. Speed to fly depends on: The object of speed to fly is to minimize the time and/or  altitude required to fly from the current position to the next  thermal and to minimize time in sink and maximize time in  lift. Speed-to-fly information is presented to the pilot in one  or more of the following ways: The pilot determines the speed to fly during initial planning  and then constantly updates this information in flight. The  pilot must be aware of changes in the flying conditions in  order to be successful in conducting cross-country flights or  during a soaring competition. Common errors regarding speed to fly are: 1.  The rate of climb the pilot expects to achieve in the  next thermal or updraft. 2.  The rate of ascent or descent of the air mass through  which the glider is flying. 3.  The glider’s inherent sink rate at all airspeeds between  minimum-sink airspeed and never-exceed airspeed. 4.  Headwind or tailwind conditions. •  By placing a speed-to-fly ring (MacCready ring)  around the variometer dial. •  Using the appropriate table or chart. •  Using an electronic flight computer that displays the  current optimum speed to fly. •  Improper determination of speed to fly. •  Failure to maintain proper pitch attitude and airspeed  control. •  Not transitioning from cruise speed to climb speed in  lift as needed and not changing to cruise speed when  leaving lift in a prudent manner. 7-38