Hi @Florent,
Welcome to the eazyBI community! 
Your calculation is missing a measure by which to count the issues and what would give it a context. From the formula, it looks you don’t need to have this calculated measure but instead you can use eazyBI predefined measure - Issues with due date. It shows all issues (both due and resolved) which have a due date specified. On the Time dimension grouped by issue due dates.(see more on the explanation of predefined measures - https://docs.eazybi.com/eazybijira/data-import/jira-issues-import/jira-core-measures-and-dimensions#JiraCoremeasuresanddimensions-Measures).
About having measures in your report you can check my presentation Jira Admin’s Journey to eazyBI from our Community Days to learn more - Presentation slides and videos from eazyBI Remote Community Day - May 14, 2020
best,
Gerda // support@eazyBI.com