We are so dependent on our Dive Computers to calculate every aspect of our Dive, yet if it malfunctions we are unable to continue diving unless we have a Safety Back-Up. Awareness of your Theoretical Depth at Altitude is Critical to Safety. This Slate will eliminate the Computing-and-Guesswork. Easy-to-Read Format for Calculations, Conversions is one side, Writable Slate on the other. High Altitude Slate is made from Durable Plastic with Emergency Phone Number for Divers Alert Network (DAN). Slate has a Slot and Eyelet for attachment of a Clip or Lanyard. High Altitude Slate makes a Great Save-a-Dive Kit Item.