Computer can only digital signal processing, can't handle die like letter.
计算机只可以处理数字信号，不能处理模似信。
2
Derivative action (referred to by the letter d) measures and responds to the rate of change of process signal, and adjusts the output of the controller to minimise overshoot.
微分动作(字母d表示)测量并对过程信号变化率进行反应，调整控制器的输出以达到最小的突出峰。
3
The bishop's letter was the signal for a campaign of vilification and intimidation unequaled in american history .