Accumulated values (months before) for reduction of current month

[#1]

I have a problem with accumulation and reduction. It's hard to explain, but I've done my best in the table below. The dimensions used are Client and Closure Date. The values I get from the load script are Consumption and Produced, the rest needs to be calculated somehow.. The most important columns are the 2 last, the other are just there for explaining the problem..

Client	Consumption closure date	Consumption	Possible reduction (80% of   Consumpt.)	Produced (for reduction)	Reduction this month	Left after reduction this month	Actual reduction incl. Acc.	Acc. Reduction left for use
								68
583244	2010-10-01	814	651	541	541	0	541	68
583244	2010-09-01	839	671	597	597	0	671	178
583244	2010-08-01	797	638	676	638	38	638	252
583244	2010-07-01	752	602	815	602	213	602	213
583244	2010-06-01	743	594	511	511	0	511	0

Please help me figure this out before I throw my pc out the window! 🙂

[#2]

To clerify..
The produced should be taken from the comsumption, but not more then 80% (the rest will be added to balance for use the next month and so on..). If production doesn't fill the 80% of consumption, then the balance will not be affected at all, however if there is a saved balance it will be added to production to fill up as much as possible of the 80%.