We all know that the speed of light is $299792458~\textrm{m/s}$. Here we use meters as measuring sticks to measure the speed of light .
But how is a meter defined? It is defined using the speed of light. Here there is a weird circular reasoning. How can this be avoided? Do we have to accept the speed of light as $299792458~\textrm{m/s}$ and not measure it at all?
