通过计算信号往返需要的时间，仪器可测定差距高度。

By timing how long the signal takes to make the return trip, the instruments can determine differences in height.

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CPU负荷增长尽管(写)事务量没有变写日志个数没有变日志文件同步的往返信号传输时间就会延长。

When the CPU load goes up, the time taken for a log file sync round trip can increase even when the number of log file syncs and the volume of redo log generated doesn't change.

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