Date Rule XML to display difference of two date in total month

Hi Frds,

This is a nightmare for me. This is first time I am dealing with date rule xml code.

Date rule has been created to display total number of month. This month would be the difference of contract end date and contract start date.

I am not having any idea of XML coding..

Please suggest. Below is the standard date rule code. now what change should I insert to display the total month.

For example:

below are the date type

Contract start date: ZST

Contract End date: ZEN

Duration: ZD

so I need to display the number of code ZD = ZEN - ZST

Attached is the default xml code in date rule.Please guide where and what code should be written.

I really appreciate with the sample code.

Thanks

Rajan