I am using this code: DATEADD(2/20/2018, -15, ‘days’) If I change out the date to reference another column it will work. When I input this, all I get are #ERROR messages. What am I doing wrong?

I need to run some calculations off of the results of a DATETIME_DIFF field. The problem is some of the fields are populated with time spans and some have NaN. I am unable to calculate anything with an NaN. My thought was to first ask if the first da...