Custom Score System in section worksheet summary?

Hi

I was wondering if anyone could help me out here.

When I visualize the worksheet summary of a section, the Final Grade is always displayed in the letter grade score system

I'm trying to costumize it since the schools in here (Portugal) do not use letter grades for anything, but I don't really find the option.

Is it possible to choose in which score system the worksheet summary averages should be displayed?

Thank you in advance.

Best regards,
Nuno Covas