The simplest and oldest type of mechanical timer is the hourglass, in which a fixed amount of sand drains through a narrow opening from one chamber to another to measure a time interval.
機械定時器的最簡單和最古老的類型是沙漏 ，其中砂排水管通過一個狹窄的開口從一個室到另一個固定量以測量的時間間隔。