Appendices useful for back of the envelop questions

Chapter Overview

In this section we have collected together resources that are valuable for solving back of the envelop problems. Some of the data in this section needs to be updated, while the web page itself may not be updated that often.
Therefore, for some of the data, you might want to do a quick search to see if more recent data exists. Some data, like the radius of the earth, is unlikely to change much.