In this paper, now published open access in the Journal of Comparative Germanic Linguistics, Joshua Booth considers the relative chronologies and interactions of two Middle High German sound changes: the lengthening of all short vowels in stressed open syllables ('open syllable lengthening'), and the diphthongisation of the high vowels /i:, y:, u:/. The paper re-evaluates the evidence of a thirteenth-century Parzival manuscript - what exactly does the scribe mean by the circumflex accent mark? - and challenges the view that open syllable lengthening triggered diphthongisation. Congratulations, Josh!