Diptych

For example, the standard notebook and school exercise book of the ancient world was a diptych consisting of a pair of such plates that contained a recessed space filled with wax.

The word diptych is borrowed from the Latin diptycha, which itself is derived from the Late Greek δίπτυχα (díptycha) 'pair of writing tablets'.

[3] From the Middle Ages many panel paintings took the diptych form, as small portable works for personal use; Eastern Orthodox ones may be called "travelling icons".

The outsides, which often received considerable wear from travelling, might have simpler decorative designs, including the coat of arms of the owner.

Large altarpieces tended to be made in triptych form, with two outer panels that could be closed across the main central representation.

The diptych was a common format in Early Netherlandish painting and depicted subjects ranging from secular portraiture to religious personages and stories.

The street artist Banksy has regularly used the diptych format for a variety of his studio produced artworks including Girl with Balloon.

A common error states that if both dials show the same time, the instrument is oriented correctly and faces north (in the northern hemisphere).

A Diptych made as stated as a combined vertical and horizontal sundial with a string gnomon will show the same time on both dials regardless of orientation.