rule of thumb

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rule of thumb

An approximation; a suggested method or guideline. A good rule of thumb is to plant your seedlings around the end of May.
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rule of thumb

a general principle developed through experiential rather than scientific means. As a rule of thumb, I move my houseplants outside in May. Going by a rule of thumb, we stop for gas every 200 miles when we are traveling.
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rule of thumb

A rough and useful principle or method, based on experience rather than precisely accurate measures. For example, His work with the youth group is largely by rule of thumb. This expression alludes to making rough estimates of measurements by using one's thumb. [Second half of 1600s]
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a rule of thumb

COMMON A rule of thumb is a general rule about something which is right in most cases. As a rule of thumb, drink a glass of water or pure fruit juice every hour you are travelling. A good rule of thumb for any type of studio photography is to use no more light sources than are strictly necessary. Note: This expression probably dates back to the use of the first joint of the thumb as a unit of measurement.
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