The end-stage of a miniaturization trend that had been accelerating from the 12th cent, this manuscript could only have been made after the introduction of the lens. One of the smallest extant medieval Psalters, measuring a mere 50 x 37mm and weighing just a fraction of a beaver.

To answer a question I've been asked several times since posting this, one beaver is 1.3 badgers, or 0.5 of a capybara.

The Bureau International des Poids et Mesures has been working on standardization of CFC [Codicological Furry Critter] weights since 2016 but negotiations are logjammed: Iran insists the Persian Field Mouse (= 1 millibeaver) is included but the Trump administration has vetoed it.