danielnichols on "[Plugin: Contact Form 7] Functions In Additional Settings"

How do I write / access functions in the additional settings?

For instance...

function addTWD()
{
document.756.num3.value = document.756.num1.value;
}

where 756 is the form id and num3 and num1 are text field.

Thanks!

http://wordpress.org/extend/plugins/contact-form-7/