Recent empirical studies about UML showed that software practitioners often use it to communicate. When they use diagram(s) during a meeting with clients/users or during an informal discussion with their architect, they may want to highlight some elements to synchronise the visual support to their discourse. To that end, they are free to use color, size, brightness, grain and/or orientation. The mentioned freedom is due to the lack of formal specifications of their use in the UML standard and refers to what is called the secondary notation, by the Cognitive dimensions framework. According to the Semiology of Graphics (SoG), one of the main references in cartography, each mean of visual annotation is characterized by its perceptual properties. Being under modeler's control, the 5 means of visual annotations can differently be applied to UML graphic components: to the border, text, background and to the related other graphic nodes. In that context, the goal of this research is to study the effective implementations, which maintain the perceptual properties of, especially, the size visual variation. This latter has been chosen because it is considered as the " strongest " among the other visual means, having all the perceptual properties. The present proposal consists of a quantitative methodology using an experiment as strategy of inquiry. The participants will be the˜20the˜the˜20 attendees of the HuFaMo workshop. They must be experts on modeling and they know UML. The treatment is the reading and the visual extraction of information from a set of UML sequence diagrams, provided via a web application. The dependent variables we study are the responses and the response times of participants, that will be validated based on the SoG principles.