The ronnametre measures 10²⁷ metres, a scale reserved for the largest structures in astrophysics and cosmology. One ronnametre is approximately 100 billion light-years, which roughly corresponds to the diameter of the observable universe. This unit allows cosmologists to discuss the expansion of space and cosmic horizons using standard metric prefixes. The symbol is Rm.
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The observable universe spans roughly one ronnametre across, though the actual topology extends further.