A primitive "app" is hidden on the bottom panel: a sliding lid revealing a hidden plate with carved spaces.
"When you draw the sliding part, there are small weights used as an assay balance," Ufuk Kocabaş, director of Istanbul University's department of marine archeology and the Yenikapi Shipwrecks Project, told Hurriyet Daily News.
Since it was a merchant ship, the tool was likely used to assess the value of some items. Assay balances were used to determine the metal content in ore or the kind of precious metal in an alloy.
Smuggled Cargo Found on Ancient Roman Ship
The notebook could have been easily carried. Each panel features four holes -- they were drilled in two pairs in order to bind the notebook together, probably by leather straps.
"Yenikapı is a phenomenon with its 37 sunken ships and organic products. I think these organic products are the most important feature of the excavations," Kocabaş said.
The sunken ship upon which the "Byzantine iPad" was found, has been dated to around the 9th century A.D.