Maas's Law

In papyrology, Maas's law - named after classical scholar Paul Maas (1880-1964) - refers to the observation that columns in bookrolls often exhibit a forward tilt such that both edges of the column gradually move to the left as the column progresses. In other words, the bottom-most line of the column of text is further to the left than the top-most line.

Johnson, William A., Column Layout in Oxyrhynchus Literary Papyri: Maas's Law, Ruling and Alignment Dots (ZPE 96 (1993) 211-215) [1]

Johnson, William A., pp. 91-99 concludes that this was deliberate and formed part of the bookroll's design.