Looks good.

> Today I’ll explain this stuff to people who know their way around computers. But I’m not one of those people! So, next time I’ll explain the nitty-gritty details in a way that may be helpful to people more like me.

I think that's a good approach, so good I was going to suggest it myself.

> smaller squares that are 1.5° × 1.5° in size:

should be 2.5 not 1.5

> 9 × 69

23 by 69

Same typo twice in both cases I think.