You bettter have one of these handy.
http://www.drugstore.com/products/prod.asp?pid=94466&catid=49223&trx=GFI-0-SRCHTS&trxp1=49223&trxp2=94466&trxp3=1&trxp4=1&btrx=BUY-GFI-0-SRCHTS
http://www.drugstore.com/products/prod.asp?pid=94466&catid=49223&trx=GFI-0-SRCHTS&trxp1=49223&trxp2=94466&trxp3=1&trxp4=1&btrx=BUY-GFI-0-SRCHTS