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The difference is known as the drift, and can be determined by the wind triangle. At least seven ways to measure the heading of a vehicle have been described. [1] Heading is typically based on cardinal directions, so 0° (or 360°) indicates a direction toward true north, 90° true east, 180° true south, and 270° true west. [1]
For practical purposes under ordinary conditions, the drift angle measured by the drift meter can be used for wind correction angle in the heading in order to put the aircraft back on the correct course, where the aircraft heading is turned into the opposite direction of the drift. [3]
Step 5. Measure length of course by using speed of 8.8 knots and converting into nautical miles via the time, speed, and distance scale; Step 6. Connect the two ends of the vectors from the current course to the course made good. Thus creating your set and drift vector; Step 7. Using the navigational triangle, place on set and drift vector.
This type of problem arises when determination of heading and true airspeed can be done by reading the flight instruments and ground track and ground speed can be found either by measuring the direction and distance between two established points of the aircraft or by determining the drift angle and ground speed by reference to the ground.
A feature's orientation can also be represented by dip and dip direction, using the azimuth of the dip rather than the strike value. Linear features are similarly measured with trend and plunge , where "trend" is analogous to dip direction and "plunge" is the dip angle.
The drift angle is marked in red. While dead reckoning can give the best available information on the present position with little math or analysis, it is subject to significant errors of approximation. For precise positional information, both speed and direction must be accurately known at all times during travel.
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To counter for the effect of Earth rate drift a latitude nut can be set (on the ground only) which induces a (hopefully equal and opposite) real wander in the gyroscope. Otherwise it would be necessary to manually realign the direction indicator once each ten to fifteen minutes during routine in-flight checks.