A small amount of this data is then used to calculate two monthly index figures, the Construction Cost Index and the Building Cost Index. Both indexes are calculated using a formula made up of fixed amounts of four components—Portland cement, 2x4 lumber, structural steel (steel beams), and labor. The only difference between the two indexes is in their labor component. The labor component of the Construction Cost Index is common (unskilled) labor, while the labor component of the Building Cost Index is skilled labor.