<P> Anton Ullrich invented the folding ruler in 1851 . Frank Hunt later made the flexible ruler in 1902 . </P> <P> The equivalent of a ruler for drawing or reproducing a smooth curve, where it takes the form of a rigid template, is known as a French curve . A flexible device which can be bent to the desired shape is known as a flat spline, or (in its more modern incarnation) a flexible curve . Historically, a flexible lead rule used by masons that could be bent to the curves of a molding was known as a lesbian rule . </P> <P> 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 . </P>

What are the lines on an inch ruler