Proper form of the "dx"Edit

I thought the proper form was to distinguish it somehow from the product of two variables named "d" and "x". One way to do this is with \mathrm{d}x instead of dx. With that in mind, I boldly went ahead and changed the article. Revert if I overstepped!—GraemeMcRae^talk 21:23, September 30, 2010 (UTC)