The Byzantine invention was found within the remains of one of the 37 ships unearthed in the Yenikapi area of Istanbul, a site which has been at the center of excavations for the past 10 years.
Also known as Theodosius Port, it was built in the late 4th century during the reign of the Byzantine Emperor Theodosius I and become the city's most important commercial port.
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Probably belonging to the ship's captain, the wooden object, whose cover is finely carved with decorations, is the size of a modern seven-inch tablet, but it's much thicker.
It consists of a set of five overlaid rectangular panels carved with frames and covered with wax. Notes could be taken on those panels, as shown by writing in Greek which is still visible on the wax.
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.
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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.
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The containers it had been carrying suggest the vessel sailed the Black Sea, transporting goods from Crimea to Kersonesos.
A research team from Istanbul University is now restoring the ship, 60 percent of which has survived in good condition, with the aim of having her set sail again by 2015.
Image: The Byzantine notebook. Credit: Ufuk Kocabaş.