I find it a bit paradoxical that those articles that aim to make calculus more approachable to everyday people are always assuming that those very people already know what the Sigma symbol means, or what [that](http://juliendesrosiers.ca/uploaded/weird-math-symbol.png) math symbol means. I see the author in this case is defining the delta and approximately-equal symbols, but I see quite a few non-obvious symbols in this article.

Maybe it's because I'm canadian or that I have not studied advanced mathematics in high-school?