From Bruce M. Metzger Manuscripts of the Greek Bible, Oxford Univ. Press

A Palimpsest provides two texts for the price of one. Because writing materials were rare and costly, medieval scribes often scraped off the writing from an old manuscript and wrote a new text over it. At left is a parchment palimpsest, with a 13th or 14th century Greek Orthodox Church service seen rightside up. Now turn the page upside down to see the faint underlying ninth or tenth century Greek text of Psalm 27 (28 in the Hebrew numeration). The text is in five columns—a transliteration of the Hebrew and four Greek translations. The first word in each column, preserved in square Hebrew letters, is the Tetragrammaton (yod-heh-vov-heh), the four-letter name of God transliterated as Yahweh. One Tetragrammaton can be discerned quite easily below and to the left of the top hole in the center of the manuscript.