II Scan the text to match the clauses together to make sentences.
A 1 Human navigators use 2 The peak elevation angle occurs 3 Thus, at local noon or midnight, latitude can be calculated by 4 When time began to be broadcast to vehicles in the 1930s, off-meridian observations of theelevation angles of two or more celestial bodies became 5 These fixes were 6 In the 1930s, hand-held bubble-level sextants were built 7 The human navigator observed 8 The accuracy of celestial fixes was 9 The first automatic star trackers, built in the late 1950s, B a measured the azimuth and elevation angles of stars relative to a gyroscopically stabilized platform. b 5–50 miles in the air, limited by the uncertainty in the horizon and the inability to make precise angular measurements on a pitching, rolling vehicle. c sun and stars through an astrodome on top of the aircraft. d to measure the elevation of celestial bodies from an aircraft without the need to see the horizon. e hand-calculated using logarithms, then plotted on charts by a navigator. f possible at any known time of night (cloud cover permitting). g simple arithmetic from a table of declination (the angle of the sun or star above the Earth’s equatorial plane). h at local noon or midnight:elevation angle (degrees) = 90 – latitude + declination. i sextants to measure the elevation angle of celestial bodies above the visible horizon.
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