Consistent units are one of the most important inventions to the modern age.
Before standardization, one used natural units such as 'feet', but these all varied from person to person.
My world abides to all natural laws of Earth and has developed very similarly.
Could anything exist naturally in my world that could serve as a consistent unit of distance measurement?
Could there be a plant, mineral or other natural occurrence that grows to a certain, consistent size?
Ideally, a unit should be roughly equivalent to a metre.