This is mainly to help me remember the way to negate the "Inconsistent Units" error but I am sure there are more people who will find this useful!!! From the real Revit master: (BTW: This can obviously be applied to many objects, not just walls as the example shows)...

Originally Posted by LRaiz (re-posted at the bottom of the discussion in this link)

"Let's assume that you are using Cost parameter available in Wall type as your unit cost. When you assign numeric value to to Cost Revit has no idea what is the meaning of this parameter. It could be cost per square foot, cost per square inch, cost per linear foot, cost per wall instance, etc. You are the only one who knows the meaning and you use your knowledge while writing a formula for calculated value in schedule. Revit just enforces that units of measurement are the same on the left and right sides of your formula.

Let say you want to compute TotalCost (number parameter) then taking into account the fact that unit Cost is also a number (no units of measurement) and Area parameter has units of length square you would write

If Cost is per square foot then TotalCost = Cost * Area / (1' * 1')
If Cost is per square inch then TotalCost = Cost * Area / (1" * 1")
If Cost is per square meter then TotalCost = Cost * Area / (1m * 1m)
If Cost is per linear foot then TotalCost = Cost * Length / (1')
If Cost is per wall instance then TotalCost = Cost

Makes sense?"