Help with MS Excel S-Curve

Hi everyone,

I am new to this forum so I would really appreciate your help in the following matter:

I have a MS Project worksheet that helped me create a Cash Flow report with Excel. My problem is that our customer has requested an "Earnings Curve" and so far I haven't been successful with the previous curves I have submitted. My due date is tomorrow

Our customer is asking for an earnings curve which will show the actual accumulative cost, base on % completion.

So far I have managed to reflect a curve that shows the actual cost, based on % completion, but it needs to be accumulative (nine is not). In an accumulative curve, the curve will always go up when their is a payment and horizontal when there is no payment. However, the curve can never go down (mine does).

Anyone can help with this?

Thanks in advance for taking the time to read my post and comments.