Cumulative interval blocks with a within-interval diagonal

What we kept from the original

A chain of cumulative blocks, one per interval, each crossed by a diagonal that states the assumption that the values spread evenly inside it.

What we changed

Chaddock's blocks were classes with their counts; ours are the four quarters between published quartiles, so every block holds the same count, and the two outer blocks stay open because the source does not say where they end.