One of the weaknesses of Tableau is that you can’t add a reference line to a chart that is based on a custom calculation or another metric within the workbook. The calcs that are offered for reference lines are good and applicable in many situations but sometimes, they are just not right. In the short video below, Joe Mako explains how to fake a custom, dynamic reference in Tableau.
NOTE: Joe directed me to his tutorial after I was asking some questions about reference lines on Twitter yesterday, I’m simply passing along his great little tutorial. Please enjoy!