IV Grammar. Skim the text to fill in the spaces with the correct prepositions.1The simplest dead-reckoning systems measure aircraft heading and speed, resolve speed __ the navigation coordinates, then integrate __obtain position. 2 It measures the direction __ the Earth’s magnetic field __ an accuracy __ 2 degrees __ a steady speed __ 60 degrees magnetic latitude. 3 The horizontal component __ the magnetic field points __ magnetic north. 4 The angle __ true __ magnetic north is called magnetic variation and is stored __the computers __ modern vehicles as a function __ position __the region __ anticipated travel. 5 Magnetic deviations caused __ iron and motors __ the vehicle can exceed 30 degrees and mustbe compensated __ the navigation computer. 6 A more complex heading sensor is the gyrocompass, consisting __a spinning wheel whose axle is constrained __ the horizontal plane __ a pendulous weight. 7 The usual speed-sensor __ an aircraft or helicopter is a pitot tube that measures the dynamic pressure __the air stream __ which airspeed is derived __ an air- data computer. 8 Hence, unpredicted wind will introduce an error __ the dead-reckoning computation. 9 Another speed sensor is Doppler radar that measures the frequency shift __ radar returns __ the ground or water __ the aircraft,__ which ground-speed is inferred directly. 10 An on-board computer resolves the accelerations __ navigation coordinates and integrates them __obtain velocity and position. 11 Attitude is computed __ a quaternion algorithm that integrates measured angular increments __three dimensions __ a faster rate than the navigation coordinates are calculated. 12 The power supply is __ front. 13 A battery is __ the case __ the handle. 14 Most accelerometers consist __ a gram-sized proof-mass that is mounted __ a flexure pivot. 15 The newest accelerometers are etched __ silicon chips. 16 The oldest gyroscopes contained metal wheels rotating __ ball bearings or gas bearings that measured angular velocity or angular-increments relative __ inertial space; more recently, gyroscopes contained rotating, vibrating rings whose frequency __ oscillation measured the instrument’s angular rates. 17 The newest gyroscopes are evacuated cavities or optical fibers __ which counter-rotating laser beams are compared __ phase to measure the sensor’s angular velocity relative __ inertial space __ an axis normal __ the plane __ the beams.
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