Set a field depending on other

I want to create a form for a race registration. The user is filing fields like birthyear, gender. Depending on these fields, an other field (read only)display the category. How can I set this dynamic field? With Javascript or PHP? Where do I put the code?

Thanks
Jan

Hi Jan,

Almost certainly JavScript and it can go in the Form JavaScript box on the Form Code tab in the Form Editor.

Bob