custom measure

Hi

I am looking to build some Custome Measure in BI to use it in my visuals.

The measure i want to build is to calculate the Movement between Actuals and Budget for Month on Month data which i have plottted.  When i start creating i could not find a "Difference" or "Variance" measure formula

1. How do i do the above

2. Is there a list of all the Measure formula that are avaialble in BI

Thanks

Nishesh