baker's dozen

baker's dozen — чертова дюжина

The popular tale behind this phrase's origin is that a medieval law specified the weight of loaves of bread and any baker who shorted a customer was in for dire punishment. So, baker's would include a thirteenth loaf with each dozen just to be safe. The story is partly true. There was such a law, but the practice of adding an extra loaf to the dozen had nothing to do with fear of punishment.

The weight and price was strictly regulated and the only way for distributors to make money would be to give the middlemen extra loaves. The baker would give the huckster a thirteenth, or vantage, loaf for each dozen. This extra loaf provided the profit for the middleman. :WordOrigins.org

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It would be interesting to track the origins of the Russian saying "чертова дюжина" (devil's dozen) back. Is number 13 considered unlucky bcs it's connected with the devil or was devil attributed to this number later? What do you think?

also
long dozen