JavaScript significant figures library: how did I do?

I'll keep this short and sweet. Tonight I wrote a JavaScript ilbrary for dealing with significant figures (adding them and multiplying them). I released it on GitHub, and I wrote some quick docs for it and a demo site on GitHub Pages. I've only known JavaScript for a year or so. How did I do with this? Is it good code, bad documentation? Bad code, good docs? Bad everything? Good everything? I want opinions.

View it here. There's a link to the demo site in the

Lemme know what you think!

Note: Moderators, I'm not just looking to promote my work, I'm only posting this because I want constructive criticism from more experienced developers.