Lengthy but difficult and interesting...
A certain king in a certain country portioned out an amount of gold to his goldsmith who was instructed to make goblets. 100 total. The goldsmith portioned the gold equally to each of his ten apprentices with the instructions they were to make ten goblets each. Each goblet was to be identical in every respect including the amount of material used.
The plot: The king discovered one apprentice was shorting his goblets by one ounce of gold each, and pocketing the stolen gold himself. It so infuriated him that he set his goldsmith before him and gave him a set of scales with the instruction that he was to discover the culprit. However because the goldsmith had hired such a man, as punishment, he was only allowed to use the scale once. Get it wrong and he would loose his life. Get it right and he would be forgiven. I have told you all you need to know. How did the goldsmith discover the thief?