This article presents a paleographical analysis of the marginal annotations that appear next to the biblical text in the Hebrew Bible codex known as Madrid M1. In order to do so, a new methodology has been developed. The ensuing analysis has identified a great number of annotations, largely located in the outer and intercolumnar margins, written by multiple hands. These later interventions have different aims and produce diverse results. The systematic additions associated with different Masoretic textual phenomena reveal an interest in organizing the information differently and offering the information on each phenomenon consistently by adding cases that are lacking. The non-systematic additions seem to be more the result or reflection of later revisions, readings, and uses of the manuscript. The annotations of both types show a clear intention to complete and expand the already abundant information found in the margins of Madrid M1, rather than an effort to correct it.