At this point, it's worth asking what benefits we achieved with the mock objects and what did they cost.

在这一环节，值得探讨我们使用模拟对象得到的收益是什么以及花费的代价是什么。

youdao

Great, but what did it cost to extract hydrogen from that water, and how much does the electrolyzer cost?

FORBES: Cars That Run On Air And Water

What did this cost us?

FORBES: Bombs Over Big Bird?

By setting up a few simple Excel formulas (nothing more complicated than addition and division, you can see what they look like in this sample spreadsheet), you can not only track your maintenance data (what the mechanics did, when they did it, how much it cost, and what the mileage was at the time) but also see your average daily mileage during each period between servicings.

CNN: Use your Mac to track your money