1. The E6B flight computer is a form of circular slide rule used in aviation and one of the very few analog calculating devices in widespread use in the 21st century. 2. These flight computers are used during flight planning (on the ground before takeoff) to aid in calculating fuel burn, wind correction, time en route, and other items. 3. In the air, the flight computer can be used to calculate ground speed, estimated fuel burn and updated estimated time of arrival. The back is designed for wind vector solutions, i.e., determining how much the wind is affecting one's speed and course. They are frequently referred to by the nickname "whiz wheel". 4. Manual E6B remain popular with some users and in some environments rather than the electronic ones because they are lighter, smaller, less prone to break, easy to use one-handed, quicker and do not require electrical power. 5. Although digital E6Bs are faster to learn initially, many flight schools still require their students to learn on mechanical E6Bs, and for FAA pilot written exams and checkrides pilots are encouraged to bring their mechanical E6Bs with them for necessary calculations. Product Category: Surface scale vector ruler flight ruler military pilot ruler flight measurement ruler E6B flight training ruler Product number: E6B Scope of application: Pilot training, internships, drills Colour: As Shown Material: Plastic Size: 9.05x4.72x0.19 Inch Package Contents: 4 x E6B aviation flight training ruler Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.