You know, if you want to measure the potential energy of something in a gravitational field, you have to define the zero somewhere, right, because it's arbitrary. You can set it anywhere you want. It's the same with enthalpy.

你知道，如果你想测量重力场,中某种东西的势能，你需要，在某处定义一个零点，对吧？,因为势能的值是任意的,你可以把它设定在。

麻省理工公开课 - 热力学与动力学课程节选

That is a maximum If you are sharing your time and energy during this period on Tuesday afternoons, or the arch-field don't work so think carefully about that.

让大家充分发挥自己的能力,如果每周二下午这段时间,你都有时间，精力也很充沛，就可以来上这门课，不过这样你就没时间参加实践活动了,所以请仔细考虑吧。

麻省理工公开课 - 电影哲学课程节选