The oldest preserved measuring rod is a copper-alloy bar that dates from c. 2650 BC and was found by the German Assyriologist Eckhard Unger while excavating at Nippur.
Ludwig Wittgenstein famously used rulers as an example in his discussion of language games in the Philosophical Investigations.
He pointed out that the standard meter bar in Paris was the criterion against which all other rulers were determined to be one meter long, but that there was no analytical way to demonstrate that the standard meter bar itself was one meter long.
It could only be asserted as one meter as part of a language game.
Anton Ullrich invented the folding ruler in 1851.
Historically, a flexible lead rule used by masons that could be bent to the curves of a molding was known as a lesbian rule.