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.