A graph of length units that have integer relations with each other

[edp (Ed Pegg)]

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[burbery1 (Peter Burbery)]

What is the paclet QuantityUnits` in the first line? Is there documentation for this paclet? I used Names["QuantityUnits*]`
to display all the functions and Information mapped over the list output, and there were a lot of rules for relationships between units.