GUI: How to change the default value of a field depending on options selected in the same form.

Hi,

I wanted my default field value to change, when i change one of my other field options.

For Ex: if i have two fields one of radio(ex vdd option --- 1v ... 2v .. 3v) and other of float. I want my float field to change its default values depending upon vdd option selected from radio field.

Regards

Neeraj