DS7's obsession with building things has finally paid off in real world understanding. We were on vacation last week and we went to several historic sites with various kinds of non-motorized machines and contraptions. DS would read the plaque in front of it to see what it was and what it was used for, then he would quietly study it for a minute and then suddenly yell put "Oh, I get it!" and explain the mechanics behind whatever the thing was. I loved the shock on people's faces when they actually paid attention to what he was saying.