TheFreeDictionary:
rule of thumb
Noun
a rough and practical approach, based on experience, rather than theory
[Collins Essential English Dictionary 2nd Edition 2006 © HarperCollins Publishers 2004, 2006]
( http://www.thefreedictionary.com/rule of thumb )


“- rules of thumb.
A useful principle having wide application but not intended to be strictly accurate or reliable in every situation
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- Idioms: 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 is a principle with broad application that is not intended to be strictly accurate or reliable for every situation. It is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination. Compare this to heuristic, a similar concept used in mathematical discourse, psychology and computer science, particularly in algorithm design. See also mnemonic.”
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Rječnik.ba:
thumb rule - praktično pravilo
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