Sounds like you should try the LOOKUP function (with a -1 as the offset):
Calculation2 =(([Total Parts] * (LOOKUP([First Pass Yield],-1))) - ([Total Parts] * [First Pass Yield])
.. to be certain .. I would create a calculated field of the previous [First Pass Yield] like this:
Previous First Pass Yield = LOOKUP([First Pass Yield],-1)
Thank you so much! I was trying to do some stuff with the LOOKUP() function too, but I think I was then trying to do additional calculations across the table/pane (or both) which clearly wasn't the right thing to do.
This worked like a charm, and now I have this in my back pocket. This type of function is really powerful and will definitely come in handy in future reports!