The disability certificate goes from 0 to 100 and is given by the social security. Depending on your general or mobility percentages you get extra helps or tax returns that barely cover the extra costs from therapy or general help.
I see nothing wrong with that slider? They are quite literally asking you if you have an official certificate and its percentage so that they can get grants by contracting you.
tbh I’m not from Spain so I haven’t come across describing disability as a number before. but because this is an official designation as you said, now this makes perfect sense
It’s not really “describing disability as a number” per se, like obviously everyone’s abilities are unique and varied, but in this context it might mean what government incentives the employer might be eligible for, and what work capacity the applicant has in terms of hours or something.