Yeah I thought about this. The only thing that stopped me doing it was how `rows` and `columns` would be utilising this private method, but `boxes` wouldn't because of it's complexity. Maybe it's just about trying to find the right name for the private method? I like `build_units`, but again in my head I hear..."well, does that mean boxes is *not* building units?".

I like the `Hash[]` syntax too, but it does look ugly around these blocks. You're suggestion does make it seem much nicer. I'll mull it over and see where we end up ;)