I'd like to add a custom field to the Contact Summary page that calculates and displays the time that the person being viewed has held a full membership.
In this case we have student, candidate and full memberships and a full member will have records for each in their membership tab, showing the transition dates from where their student membership ended and candidate membership started, where the candidate membership ended and their full membership started.
For the "Years as Full Member" custom field, we want to be able to glance at the summary page and see that a member has held a full membership for 9 years, 12 years, 25 years, etc... The calculation is simple enough but I don't know how to integrate it within CiviCRM/Drupal.