allocate supply to demand by SKU

[gopyle]

Hi - I need to allocate supply to demand based on the order that the demand is shown.  The supply will waterfall from one order to the next until the first supply is completely depleted, and then proceed to the next supply. The first supply must be completely assigned before moving onto second. It is possible to have the orders filled by multiple supplies.    The orders must be filled in the order they appear (presorted by RDD date and Business priority)

I am trying to build an iterative macro that loops around until all supply is decremented, but need to know how to add a column for each iteration that shows the prior allocation

Thank you in advance for your assistance.