And so, there is the distinction between fixed schedules versus ratios, variable schedules and ratio versus interval.

因此，在固定时程与变化时程之间,以及在比率与间隔之间，存在着一些区别。

耶鲁公开课 - 心理学导论课程节选

Change the independent variable, find the change in the function, take the ratio and that's the derivative.

改变自变量,算出函数的变量,计算比值,这就是求导

耶鲁公开课 - 基础物理课程节选