Wikipedias answer to the diptych

A diptych (pronounced "dip-tick" IPA: [ dip'tik] (or US: [ 'dɪp.tɪk ]) from the Greek δίπτυχο [ ði'pti.xo ] di- "two" + ptychē "fold") is any object with two flat plates attached at a hinge. Devices of this form were quite popular in the ancient world, types existing for recording notes and for measuring time and direction. The term is also used figuratively for a thematically-linked sequence of two books.

It is in this form that the mention of "diptychs" in early Christian literature is found. The term often refers to official lists of the living and departed that are commemorated by the local church. The living would be inscribed on one wing of the diptych, and the departed on the other.


A diptych is also a type of icon whereby two panels are joined together with a hinge, so that they may fold together for protection when travelling, and then be unfolded for veneration when one's destination has been reached. Such diptychs are also called "travelling icons".
second thoughts: (I should have called this blog Travelling Icons)

The other form was a portable sundial:

interesting