XS Scuba Folding Wrist Slate. 

Features: 

• Designed to fit the curve of a forearm
• Three separate writing surfaces with two fold up leafs
• Carbon stick pencil
• Dimensions 4.25" wide x 4.0" tall  (10.8 x 10.2 cm)
• Two methods for attachment included: Velcro strap and bungee cords