The history of English spelling is an eventful one, from Old English with an almost one-to-one sound-to-spelling relationship, to Modern English, notorious for its sound-to-spelling unpredictability. In between lies a vast period characterised by immense spelling variability, reflecting the cumulative effect of dialectal variation and lack of uniformity, additionally compounded by the mode of text transmission in the manuscript culture, whose characteristics were adopted in a wholesale fashion into the culture of early print. In effect, early printed books present a rich kaleidoscope of spelling variants, which – not infrequently – co-occur on the same page or even in the same line of a printed text. This paper addresses the issue of this variability with a view to measuring in mathematical terms the degree of internal spelling variation within a text and showing that much of the spelling variation is associated with compositors as agents in the printing process. The analysis of internal spelling variation is based on George Joye’s 1534 English translation of the Psalms printed in Antwerp and aims at identifying parts of the text which are similar or different in terms of spellings by applying cosine similarity measurements performed on individual quires of the publication.