1. What is a good and safe (and cheap) way to whiten teeth? Mine aren't bad, I've seen much worse, but I'd like to make them just a little bit whiter. A lot of stuff that's sold in stores is really expensive and I've heard can be harmful for your teeth (wears down enamel or whatever). Any suggestions?
2. When did minute hands on clocks first get used? And how available were they to regular people when they did first start getting used?