一、导言物理学的三个基本量中,质量标准和长度标准的保持在技术上比较简单,只要用适当的材料做成标准砝码或量尺就能够永久保存使用.时间标准的保持要困难得多.以地球自转周期为基准的平均太阳时〈UT〉和以地球公转周期为基准的历书时〈ET〉每测对一次,都要化上一个月到二三年的时间,因此对天文测定时间的保持就更显得重要.由于频率(单位时间 I. INTRODUCTION Of the three basic quantities of physics, the maintenance of quality standards and length standards is relatively technically simple, and can be permanently stored using standard weights or measuring tapes made of the appropriate materials. Much more. The average solar time based on the earth’s rotation cycle is and the solar cycle time-based almanac is measured from one month to two or three years. Therefore, It is even more important to maintain the measurement time, because of the frequency (unit time)