In early times measurements were made by comparing things with parts of (example). Early units of measurement included the distance from the elbow to the fingers, the width of the hand and the width of the fingers.Some of these human measurements are still used. For example, 66 based on the length of half the thumb. A foot was originally 67 of a man’s foot. A mile was one thousand walking steps. These units were only 68 because their standard—the human body—was not constant. Governments tried to 69 them by using rods of fixed lengths. But these rods still varied from 70 to country. During the French Revolution, scientists looked for a 71 which did not change. They chose the distance from the Equator to the North Pole, which is one quarter of the circumference of the Earth. One ten millionth of this was called 72 and became the basic unit of the metric system. Other metric 73 are based on it. For example, the centimeter is one hundredth of a meter. A gram—the unit of 74 is the mass of one cubic centimeter of water.A standard meter was marked on a platinum bar. The accuracy of 75 was checked by comparing them with this bar. Nowadays the meter is standardized by comparing it with another constant—the wavelength of a certain kind of light.66. ______ 67. ______ 68. ______ 69. ______ 70. ______71. ______ 72. ______ 73. ______ 74. ______ 75. ______ 暂未登录
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