When I use cascading dynamic field, the text in the field is correct, but, when I try to calculate between two of them, the result is wrong because the used data are the "id" of each.
I tried changing value option, but the field shows multiple choices instead a single data...
Calculation is made on value of the fields, not id. To use text, you would need to create custom attribute starting with data- (e.g. data-text) in your select dynamic cascades and populate it with your text. Then you can use this attribute in computations (check Custom Attribute at bottom and enter part after data- in the box next to field)