A rule of thumb 指依据经验、而非精确计算得出的简单实用准则。它通常有用，但存在例外。这个表达语气中性，既能用于交谈，也能用于作文。
什么情境适合说 a rule of thumb？
写一句英语，检查习语是否适合当前情境，以及哪里需要修改。
本次检查比平时稍久，完成后反馈会自动显示在这里。
as a rule of thumb, + clause; a good/useful rule of thumb is to + verb; a rule of thumb for + noun
- As a rule of thumb, I get to the airport three hours before an international flight.
- A useful rule of thumb for exams is to spend five minutes planning each essay.
- My grandmother's rule of thumb was simple: never go food shopping when you're hungry.
修改原因
修改前As a thumb rule, drink a glass of water with every cup of coffee.
修改后As a rule of thumb, drink a glass of water with every cup of coffee.
容易把它当作普通复合名词组合成 thumb rule。常见英美英语中的固定表达是 rule of thumb，放在句首可以说 as a rule of thumb。本页练习采用这一形式；thumb rule 在常见英美用法中不如它自然。
不要和 as a rule 混淆，后者表示“通常”：As a rule, I walk to work。As a rule of thumb 则引出大致的实用建议：As a rule of thumb, save a tenth of your income。在严格的学术写作中，也可以用 a general guideline。
动手练习
Spending no more than a third of your salary on rent is only a rule of thumb, so treat it as a ___ guide.
查看答案
rough — Only a rule of thumb 强调这只是大致的经验建议，所以选 rough guide。Strict 表示严格的规则，与这里保留例外、仅供参考的意思不符。
分享一条你在学习、工作或日常生活中遵循的实用准则。以 as a rule of thumb 开头，并说明它怎样帮助你。
As a rule of thumb, I learn ten new words a day, because a small daily goal stops me from giving up.
练习把新词用准确
用正在学的词造句。LetsWords 检查用法和语法，提供修改与母语解释，再通过复习巩固。