While trying to consider why they might have selected 60 I started to wonder where the prime factors went, or rather might have come from; since it's already cl

While trying to consider why they might have selected 60 I started to wonder where the prime factors went, or rather might have come from; since it's already clear why they were useful for divisions. Dividing a circle into quadrants consumes 2 and 2, and is similar to folding. Similarly 3 (like the thirds letter for envelope technique) could be the next granularity of folding. Finally the 5 is short enough that some straw or string bent enough times to divide it into fifths could approximate sufficiently useful precision.