Calculate the difference between cumulative value

[DominiC181]

Hello everyone.

I work with cumulative data in my app (cumulated in one year)

Need to calculate difference betwwen cumulative values.

I have created date line like 2020-12, 2021-01, 2021-02 etc and I have tried to created difference in data load editor like this

Amount - Previous(Amount) as Amount_diff,

This is not work for turn of the year - new cumulation begins in next year.

Can you help me?????