A test of a newly trimmed pen nib, termed probatio pennae in Latin. A quill pen requires recutting very frequently (at least twice per folio). Catch phrases, names, letters, and sketches were often written in the margins or on flyleaves to test the recut nib, or simply as doodling.
تجربة قلم; تمرين خطّي
Essai de plume
Prova di penna
Probatio pennae; Prueva de pluma
Michelle Brown, Understanding Illuminated Manuscripts (Malibu, CA: J. Paul Getty Museum in association with the British Library, c1994).