Get the first value of sum function

[KIdriss]

Hello,

I would like to know how to compare a value of a yearQuarter compared to the first yearQuarter.

- Dimension: colDate.autoCalendar.YearQuarter

- Measure:  comparison with the reference

I tried this but i get nothing:

( Sum(traf_aer_pax) - Aggr(Sum(traf_aer_pax), periodData.autoCalendar.YearQuarter) ) / Aggr(Sum(traf_aer_pax), periodData.autoCalendar.YearQuarter)