Hi Kadoryz,
please look at this example.
So, we have data processor with a tabular part (scr 1). The tabular part has an attribute with the Number type (screen 2).
Then we create a form for our data processor and place the tabular part on the form (scr 3). Also, for the tabular part, enable the "Footer" checkbox (scr 4).
Then we do the following steps (screenshots 5 and 6).
After these settings, the totals will be calculated automatically (scr. 7)