A third area is building data systems that not only measure student success, but also inform teachers how to improve.

VOA: special.2009.07.30

Often, for a particular state change, it is easy to calculate two of these, but not the third.

对于一些特定的状态变化，它们中的两个很好计算，但是第三个往往不容易计算。

麻省理工公开课 - 热力学与动力学课程节选