This last equation determines the development of the capital stock over time. The equation set up for the PIM at the end of a year(t). 2.An alternative to the PIM is the OHSM. In macroeconomics, investment consists of the additions to the nation's capital stock of buildings, equipment, software, and inventories during a year. After completing this course, City of Tucson staff are also qualified to take advanced SmartScape courses including Urban Forestry and Green.