hi just wondering if other community members do assembly builds from items that can be variable and how they handle that?

We build an assembly from a product that can vary due to atmospherics, temp etc. We currently do a stock take of the product used for the build and then from sales reports work out how many assemblies we need for sales and the divide the item stock inventory by the no of assemblies needed for sales and juggle the figures to make the item used in the build figures volumes work, this is not an easy task. Could we build the assemblies using an average that the assembly needs and put the variance using inventory adjust to either the item cos or should it be to shrinkage & loss expense.

Appreciate any help.