Calculated Key Figures for calculate the accumulated value of year

Hi experts,

I want to make a report with the acumulated value of Net Value (0NETVAL_INV) of Invoicing.

In the report, I am restricting for one month and I am reporting the Net Value, but I want to see the acumulated value from January to the selected month too.

I know I have to use a Calculated Key Figure and Variables but I don`t know which are the step for this issue. I have read a lot of documentation but there are not clear steps to follow.

Could someone give me some tips for this issue?

Thanks