There is a credit card size-like "tip table" for your wallet. Also there are freewares available on line to download (upload) to your pocket PC such as a I-Phone, Palm, etc.  Otherwise, using the calculator function on a cell phone works too.  But here is a link to the wallet size tip table.  Order it at a cost of a buck each for a minimum of five.  You may lose it and need it again, so if you plan to order them, keep one in your possession at all time and whip it out when you need it.

http://tiptable.com/