I pulled some dates of the internet for the holidays for the rest of the year. I've made a standard deviation that runs throughout the year and one that is set for the entire year. We use WINDOW functions for this as they allow us to use table calculations and base aggregations (which a standard deviation is) on on other aggregations (table calculations). The attached workbook is in Tableau 9.0 and can be opened with any later edition.
This is perfect. The way you calculated the day difference is so much more elegant that the work around I was using. This answer is exactly what I am looking for.
Thank you very much.