Has it been awhile since you last practiced some of your underwater hand signals? The Recreational Scuba Training Council – which includes IDEA, PADI, PDIC, SDI, SSI, and the YMCA – has produced a nifty little PDF that you can download and review.

An old instructor tip for stuff like this that you might like to save and have available in your gear bag to review from time to time is to print the pages out and then go to your local Kinkos and have them heat laminate the pages. They won’t stand up to taking them on dives with you but you don’t have to worry about them getting ruined by a few drops of water either.