What a precast concrete factory needs to control
A precast concrete product starts out just like ready mix: cement, aggregates, admixtures and water according to a mix design. The difference is that the concrete doesn't leave in a truck but turned into units, and more time passes between buying the raw material and selling.
That's why materials matter so much. If you don't know how much cement and aggregate you have, what that stock is worth and what each mix design really costs you, the price of what you sell is worked out blind.