  In the field of information visualisation, Euler diagrams are an important
tool used in various application areas such as engineering, medicine and social
analysis. To effectively use Euler diagrams, some of the wellformedness
properties needs to be avoided, as they are considered to reduce user
comprehension. From the previous empirical studies, we know some properties are
swappable but there is no clear justification which property would be the best
to use. In this paper, we considered two main wellformedness properties
(duplicated curve labels and disconnected zones) to test which among the two
affect user comprehension the most, based on the task performance (accuracy and
response time), preference and eye movements of the users. Twelve participants
performed three different types of tasks with nine diagrams of each property
(so, in total eighteen diagrams) and the results showed that duplicated curve
labels property slows down and trigger extra eye movements, causing delays for
the tasks. Though there is no significant difference in the accuracy but the
insights obtained from the response time, preference and eye movements will be
useful for software developers on the optimal way to visualise Euler diagrams
in real world application areas.
