How to allocate the sum of total depreciate into a month in the report Fix Asset Net Value( FA613000) ?

I want to allocate this amount over the months. Does anyone have any ideas on how to write a function to divide the total allocated amount?

I used the formula =SUM(iif(left([FAHistoryByPeriod.FinPeriodID],2)='01'and right([FAHistoryByPeriod.FinPeriodID],2)=right([@PeriodTo],2),[FADetails.AcquisitionCost]/(12[FixedAsset.UsefulLife]),0) ) but the report is not showing correctly.*

The correct value is 6 months with 6 equal values but it only shows 3 months, or 1 month.