[_sh]

"Fill in your job title. If you are unemployed or a student, put N/A."

Hardly equation solving.

[kstenerud]

Job Title: ___________ [ ] I am unemployed or a student

Checking the box disables the job title field.

You don't need to make user interfaces that behave like paper forms.

[icebraining]

Agreed, as long as the checkbox comes before the field, to avoid wasting time filling in fields that will be ignored anyway.