Creating a Do Until loop

[pld]

Please see the attached simplified version of my spreadsheet (Notes included). I'm desparately looking for a macro, the DO UNTIL and LOOP functions, which will take the cell marked in orange up in iterations 0.0001 and stop when the number in yellow is reached, in Column C.

I've been looking at VBA for the past week and I'm affraid I'm none the wiser. Unfortunately the Solver does not work on my original spreadsheet because it is a non-smooth model.

Thanks all.