Offset Time Series visualization based on page level filters

I deal with time series of targets deformation and what I need is not their absolute position but the relative change from to the beginning of my analysis that I define by the page level filter (in Advanced Filter Mode: date is after...).
I have many targets and all of them should start from zero at the beginning of the line graph visualization (to optimyze the Y-Scale space and allow the relative movements assessment).
I tried to calculate a new column with DAX (based on the measure of FIRSTNONBLANK value) but I'm not able to fix the context to the value (and corrensponding row) that I've set in the filter. In excel it's easy (a couple of "$" are enough), here it's very hard: the measure remains dynamic while I want to fix it for every target so to get: RelativeValue = AbsoluteValue - ValueAtTheFilteredDate.