We are interested in understanding how digital ink and speech are used together in presentation. Our long range goal is to develop tools to analyze the ink and speech channels of recorded lectures. As a first step in this process, we are making a detailed study of instructors’ digital ink usage in real university lectures. This work is being done in the context of a Tablet-PC based presentation system we have developed, but is applicable to other systems which record digital ink and speech. In this paper we concentrate on how instructors draw and use diagrams in the process of lecture delivery and identify phenomena which are important when automatically processing the diagrammatic ink.