Don't forget to buy some kleenex before you give someone this gift! This is a phenomenal idea for a birthday gift. Definitely one that would never be forgotten and could be passed down. I wish I would have thought of this long ago foru parents.
This site is great for those formulas that we may not be so familiar with. Enter you math problem and it takes you step through on how to get the answer. Wonderful for that extreme advanced math. (For my kids, at least, since I'm a math-a-holic and tend to give him the most nerdiest explanation possible.) LOL Or so my Trevor tells me!