Explaining Value Added -- Dickeson

We're using crew hours that we guess for scheduling. Finally, we're using real dollars of materials actually consumed, plus crew hours actually worked, multiplied by rates we've configured by assumptions for comparisons.

Whew! I'm confused. For estimating, why don't we just stick with the real dollars of materials? You know, when you look back at those ratio values, that's really what were doing to arrive at a price, isn't it? Otherwise why would materials be so consistent as a percentage of manufactured sales over the years?