Campaign Tracker also supports up to six custom variables. Use these to capture any other variables that you might be using in your URLs. This is helpful in a number of situations, including in situations where you’re using Adwords and want to leave auto-tagging on. Adwords allows you to add extra variables in the URL interface, when creating your ads.
How it works
For example if you have a URL like
http://MyDomain.com/?samplevar=aTestValue
You can setup samplevar to be collected by the plugin and passed through your form.
The screenshot here shows the setup for this example.