Before revision: Likewise, the stock at some time t is the integral of the flow from some time when the time was zero until time t. For example, if the capital stock is increased gradually over time by a flow of gross investment and decreased gradually over time by a flow of depreciation , then the instantaneous rate of change in the capital stock is given by where the notation refers to the flow of net investment, which is the difference between gross investment and depreciation.
After revision: Likewise, the stock at some time t is the integral of the flow from some moment set as zero until time t. For example, if the capital stock is increased gradually over time by a flow of gross investment and decreased gradually over time by a flow of depreciation , then the instantaneous rate of change in the capital stock is given by where the notation refers to the flow of net investment, which is the difference between gross investment and depreciation.