Excel PowerPivots: Need help with Calculate Measure

Excel Version:  Excel 2010 PowerPivots

Problem:  I'm relatively new at PowerPivot Measures but have some experience.  I'm trying to write a measure using the Calculate function which will generate the report, as noted below, from the PowerPivot Data Table, as noted below.

I want to be able to set the pivot table's page filter for "Year" to 2013 (in this example) and generate a report which will show the following information summarized for each contract:

1. The Unbilled Portion-Beginning of Period (at beginning of year selected) for each contract.
2. The Total New Contract, Added Work and Amount Billed for the year for each contract.
3. And the Unbilled Portion-End of Period for each contract.

Here is a link to an Excel file which has the info in the screen shot along with a few of my feeble attempts to write the correct Calculate formula. 

Any help would be greatly appreciated.  I have Jelen's and Collie's books on PowerPivots and neither helps.  They don't give anything but super simple examples.

Regards,

...bob

Bob Sutor