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Wittgenstein's ruler: Unless you have confidence in the ruler's reliability, if you use a ruler to measure a table you may also be using the table to measure the ruler.

Nassim Nicholas Taleb (2008). “Fooled by Randomness: The Hidden Role of Chance in Life and in the Markets”, p.224, Random House
Wittgenstein's ruler: Unless you have confidence in the ruler's reliability, if you use a ruler to measure a table you may also be using the table to measure the ruler.